Rainwater Harvesting System Installation

February 1, 2015

Why did we choose to install a 5,000 gallon tank (technically 4,995 gallons) for our rainwater harvesting system?  The short answer is because that’s what made sense for us.  We’re using the rainwater to flush the toilets and for the cold water laundry.  We estimate this volume to be around 6,000 ~ 8,500 gallons per year (roughly 500 ~ 700 gallons per month).  So, we could have installed a much smaller tank, say 600 gallons if we wanted to.  But when we looked at the cost of installing the system (this includes tank, pipes, filters, fittings, labor, etc.) the cost of the tank is just a fraction of the total system cost.  Most of the cost is in the labor.  So why not get a large tank?

But not so large.  The reason why manufacturers sell tanks sized 4,995 gallons (just a shade smaller than 5,000 gallons) is because of the building codes.  Above ground rainwater harvesting tanks larger than 5,000 gallons need to be placed on a foundation or platform.  Tanks smaller than 5,000 gallons can simply be placed on a bed of gravel.  Thus, we opted for the 4,995 gallon tank that will allow us to capture larger volume of rainwater during the winter without having to build a special foundation for it.

The amount of rainfall in Santa Cruz has been highly variable in the last 7 years.  I invite you to take a peek at the data from WeatherCat website which shows the annual rainfall in Santa Cruz ranging from 15 inches to 34 inches annually.  We’re grateful that this private weather station located just 2 miles away from our house provides us with lots of useful detailed climate data, much better than what we could do for ourselves.  Thanks WeatherCat!  So, how many gallons of water can be harvested from 15 – 34 inches of rain on our rooftop?  It depends not only on how much rain we get but also on the roof area.  We have most of the gutters (about 3/4 of the total roof area) directed towards the rainwater tank.  This means 15 – 34 inches of rain per year can yield between 14,000 to  32,000 gallons of water.

By the way, the rule of thumb is 1 inch of rain yields about 600 gallons for 1,000 square feet roof.  To get the precise conversion of inches of rain to gallons of water simply plug in the figures in this calculator.

Santa Cruz Municipal Utility bill tells us that our annual water usage (Apr 2013 – Mar 2014) is pretty low — 38 CCF or 28,424 gallons for everything.  This includes water used for toilets, cooking, bathing, laundry, watering the garden, etc.  What this means is that even if our roof areas is capable of capturing over 30,000 gallons of rainwater on a very rainy year we won’t be able to use all of it.  Trying to maximize storage for our roof area is an overkill.

Rainwater Tank

The 4,995 gallon tank comes in 2 different shapes — tuna can or the soup can.  Easy to imagine them right?  The tuna can is wider and shorter than the soup can and it fits nicely into the corner of our yard where the dark green tank blends in with the trees.  The model is Bushman CWTX5-132 which measures 10-feet 9-inches in diameter and 8-feet tall.  It looked huge when it arrived on Jon Ramsey’s trailer on a July morning.  They said that it barely cleared some of the bridges and freeway overpass on the way.  It rolled easily down the driveway into the backyard.  The team from AquaSoleil was busy in our back yard for a few days.

rainwater tank delivery
Getting it placed properly in the corner of the yard was a bit tricky — 4 men rolled and turned the tank along the temporary skids positioning the tank just so.  Micro adjustments were made before the tank was tipped over right side up.  Experienced eyeballing enabled the guys to place the tank so that the openings would be aligned with the pipes in the trench.

skids to position the tank

Now let’s follow the path of the water, from the rooftop to the tank.  Rain from 1,503 square feet of roof is directed to the rainwater tank via the roof gutter and underground pipes that makes its way over to the back corner of the yard.  The rest of the roof area feeds rainwater to the rain garden next to the tank.

Gutters, Leaf Screens

Since there are no tall trees next to the gutters we weren’t worried about having fallen leaves clog up the gutters and the downspouts.  Still, there were gritty sand-sized debris accumulated in the gutter when we took a look one week before the rainwater system installation.  To make sure we get clean water into the tank we cleaned out the gutters thoroughly by hauling the shop vac onto the roof and vacuumed it.

clean gutters

RHINO Gutter Guard was installed over the gutter.  This will keep the gutters clean.  No more cleaning gutters!

Rhino Gutter Guard

Rain collected in the gutters flow down through the 2 screens from the downspout into the pipe that conveys water to the tank.  In case you’re wondering, this was in place before the Rhino guard on the gutters.  Now that we have screens directly on the gutters we really don’t need the leaf screens but it’s there just in case.

leaf catcher in the downspout

Fittings, Connections

The pipes that convey rainwater from the house to the tank in the backyard were installed 3 years ago during the installation of the french drain.  3-inch PVC pipes are buried 18-inches below grade and gently sloped down across the yard to where the rainwater tank is.  Also installed 3 years ago were the electrical conduit to power the pump and the 1-inch rainwater supply line (purple pipe).  The open ends of these pipes were covered with duct tape.  When the rainwater system project came along we found some debris in the pipes since the duct tape fell off.

In the photo below the green pipe on the right (without any valves) is the overflow to the rain garden when the tank continues to fill beyond capacity.  The green pipe on the left conveys rainwater from the roof and fills the tank.  The two valves in the picture will either let the water pass or not.  When we want the rainwater to fill the tank the upper valve will point upwards and the lower valve will be in a horizontal position to prevent water from draining directly into the rain garden.  When the tank is full and we want to simply direct the rainwater straight to the rain garden the valve positions will be reversed — upper valve in horizontal position and the lower valve pointing down. (Note:  The position of the valves in the photo below shouldn’t be used because the rainwater will never fill the tank.)

Rainwater tank

The green hose coming out from the bottom is feeding the water from the tank into the pump.

Outlet from rainwater tank
water filter and meter installed


Inside the lavender box in the above photo are the water filter and the water meter.  EZ Kleen Y-filter is installed to remove debris before the rainwater goes into the pump.  The removable cartridge is easy to clean.

EZ Kleen 100 micron Y-filter

Water Meter

This Netafim M series water meter is used to measure the amount of water that flows from the pump into the house.  This was installed to measure the volume of rainwater used inside the house for toilets flushing and cold water laundry.  On a monthly basis a field crew from Ecology Action comes by to take measurements and water samples.  Thus far they’ve told us that our rainwater is pretty clean.

Netafim M-series Water Meter


Grundfos MQ 3-45 pump turns on automatically when it detects water flow and shuts off automatically when water ceased to flow.  So it only turns on when we flush the toilets or when the washing machine calls for cold water.

Grundfos MQ 3-45 pump

Notice the rainwater spigot is painted purple and the tag clearly says non-potable water.  If you happen to visit our yard please don’t drink this water!

Rainwater Spigot

Connect and Test

Since there were 2 different companies involved in installing our rainwater system infrastructure we asked both to be present when we did the initial test.  Back in 2012 Santa Cruz Green Builders installed the dual plumbing to the toilets and washing machine inside the house as well as the underground infrastructure in the yard.  In 2014 AquaSoleil installed the tank, pump, and the fittings.  

It was a dry August week with no chance of rain when we did the installation.  So the tank needed to be partially filled with city water supply to do the end-to-end test.  First part of the test was to see if the water from the gutter will fill the rainwater tank.  This was simulated by taking the garden hose and running the water into the downspout.  This test removed all doubt of whether gravity feeding was adequate to fill the rainwater tank or not.

Pour water into downspout for test
Rainwater tank is filled

The cutover from city water source to rainwater source was easy.  First, the city water valve was turned off and the hose connected to toilet tank was switched over to the rainwater side.  Before connecting the hose to the toilet, accumulated debris (dirt and mulch) was first flushed out from the pipe that sat dormant for 2 years.  Flushing out the debris proved that the pump was working. When the water ran clear for a minute or so the hose was connected to the toilet.  I had the honor of pressing the button on the Niagara Stealth toilet for the first test and it worked!  So now, we just need to wait for the rain.

And we did get a little bit of rain in September.  Less than an inch but it probably deposited about 400 gallons in our rainwater tank.  Optimistically expecting more rain in October, we switched our toilet line from city water to the rainwater supply on October 1, 2014.  Hurray!  All done, right?  Well, not really.

Backflow Prevention

In mid-October we learned that the rainwater system project was not truly done.  Not until the paperwork is finished with the water department, anyway.  We received a call from them asking us if we had a back flow prevention device installed.  We didn’t and we hoped we didn’t have to.

Backflow prevention device is installed to protect the potable water supply.  If there is a condition on the property that has the potential for untreated water (rainwater in our case) to flow back into the water department’s supply line then a backflow prevention device must be installed near the utility’s water meter on our property.  In our case the potential exists because we have a pump that conveys rainwater to the toilets and washing machine.  If a cross connection was made to connect rainwater to city’s potable water (which we wouldn’t do because we won’t be able to flush the toilets) and the city’s water pressure dropped because a nearby fire hydrant was hit by a bus (which I’ve seen happen last year) then our non-potable rainwater could get into the city’s water supply.  It’s a very remote chance  but our water department is vigilant and have a good track record for installing backflow prevention devices.

Below is a photo of a small backflow prevention device.  Once I recognized this for what it is I started seeing them everywhere — in front of medical buildings, shopping malls, commercial buildings, schools, etc.  The presence of the backflow prevention device means there’s some potential at the property for non-potable water to get into the water supply.  Typical things that raise a red flag are radiant floor system, solar thermal system, and pump of some kind.  Some of the backflow prevention devices on commercial properties are huge — diameter of the pipe being the size of a large tree trunk.  Besides the additional cost to install the device there is an annual cost associated with having this on the property — annual inspection must be made by a certified professional who charges for such inspection.  But mostly I didn’t want this in our front yard because I didn’t want it to deter other people from doing a rainwater harvesting project like ours.  It’s a simple concept and the implementation should be simple too.

Backflow prevention device

I invited the inspector to come take a look at our installation and discussed the approach used by another site doing the same rainwater application over at the Live Oak Grange.  They have the system set up so that the rainwater lines are permanently connected to the toilet, thus eliminating the need for switching the lines back and forth between city water and rainwater.  The city water feeds the rainwater tank when the water level gets low using a float and a valve triggered by the float. ( This is just like how the toilet tank is filled using a float and a valve.)  The key to this setup is to show that there is an “air gap” between the city water supply and the rainwater tank.  

I told the inspector we will be doing the same and he agreed to this approach.  When he came back again to look at the completed setup of the “air gap” he was satisfied and signed off on the paperwork.  He’ll be making a visual inspection of the air gap on an annual basis.

Here are some photos from the installation of the air gap and testing to make sure it works.

When the water level is down the float pulls the string and the valve opens
When the water level is up the float shuts off the valve

There is an air gap of 3 inches between the valve (blue) and the top of the tank

We started using rainwater for toilet flushing on October 1, 2014.  After the big storm in December our rainwater tank was full so we switched our cold water line for the washing machine on January 5, 2015.  We haven’t noticed any difference in the quality of laundry.  So far so good!

Rainwater for Indoor Non-potable Use

Yay!  We got the permit for our rainwater harvesting system for indoor non-potable use.  Up until now we’ve focused our attention on thermal comfort and energy consumption in our home.  Now we shift our attention to water — the precious natural resource we can’t live without.  In this post I’ll share the background of how we got here on our green journey and why it’s important.

Most of you know that California is in the middle of a drought right now.  When I read this article in New York Times I was reminded that residents of Santa Cruz have been practicing water conservation for a long time, ever since the drought in the 1980’s.  The effect of the conservation effort is reflected in the current volume supplied by the local water district:  30% less today than it was in 1987.  Unlike San Francisco and nearby cities in the Bay Area, Santa Cruz is not connected to the California Aqueduct and we don’t have water piped in from remote sources.  Our drinking water comes from local sources and residents here are not a fan of desalinization so we make do with less water per person.  On May 1, 2014, new rationing allotments and progressive surcharges went into effect.  For single family homes this means 249 gallons per day (assuming 4 people living in the house) or 62 gallons per person per day.  For the 2 residents of Midori Haus the allotment comes out to 124 gallons per day.

Currently we are using well below the allotment amount.  Let me show you our recent water bill.  By the way, I used to simply file away the water bill after I paid it and haven’t paid much attention to the data.  The current drought condition got me curious about typical usage volume and for what purpose.  If you’re also curious have a look at the middle portion of this page on Sierra Club’s website that shows the breakdown of household water use.  I’m sharing my utility bill here with you as food for thought.  I invite you to pull out or download your water bill and simply notice how much water your household uses.

Last month (May 2014) we used an average of 52 gallons per day (only 43% of our allotment) and our annual average water consumption was 82 gallons per day (66% of our allotment).  I’m pretty happy with our our low water usage.  And we’re not super frugal about our behavior.  We do about 8 loads of laundry per week, run the dishwasher almost daily, prepare 2-3 meals at home daily, and I’ll even confess that I’ve never outgrown the teenage syndrome of long showers.  The main reason why we have low water usage is because we don’t have a lawn and most of our trees have tapped into the water table under the soil so we don’t water them.  It also helps that we have super efficient water appliances and fixtures in the house.

In a separate post I’ll show you the different components of water saving features we have in the house today.  For now let me explain what we mean by non-potable use of rainwater catchment system.

Non-potable means not suitable for drinking.  So what are the uses of non-potable water inside the house?  Toilet flushing and laundry.  At this point I invite you to pause and think about the water used to flush the toilet.  Water is extracted from the ground, river, or reservoir then treated to make it safe for drinking at the water treatment plant.  Then the clean drinking water is pumped through the network of pipes from the water treatment plant to your home.  When you press the button or the handle on your toilet to flush the pee or poo you are using clean drinking water to transport them to the sewage treatment plant or into your septic tank.  Hmm.  Seems like a lot of energy and resources are expended to flush the toilet.  So, what if you collected a portion of the rainwater falling on your property and used that instead to flush the toilet?  That’s what we’ll being doing.

The notion of using rainwater to flush toilets and doing laundry is no longer exotic.  The indoor non potable uses of rainwater is spelled out in the California Plumbing Code now.  Chapter 17 of the 2013 California Plumbing Code describe the requirements for non-potable rainwater catchment system.  Note that even if it is part of the plumbing code the building officials doing the plan check may not be as familiar with this yet so they may grace you with extra scrutiny.  For us it wasn’t an over-the-counter permit and it cost us over $900 for the permit.  Let’s hope that the permit process will be faster and cheaper as it becomes mainstream.

How did we get the inspiration to do this?  About 3 years ago we visited the dormitory at the Green Gulch Farm at the San Francisco Zen Center for a Passive House Tour.  It was there where we first saw the installation of rainwater harvesting system to flush toilets and to do laundry.  We’ve been wanting to do this at Midori Haus but the details of the permitting process wasn’t clear when we were in our home remodel construction phase.  So had some pre-plumbing put in place and we decided to shift the implementation of the rainwater system to a later phase.  (Remember, this was before the 2013 California Plumbing Code update).  When we learned about a local program to evaluate the water quality and cost effectiveness of non-potable rainwater harvesting system for indoor use we jumped on it.  We filed our application with Ecology Action, a local environmental nonprofit organization, back in October 2013.  In January 2014 we were delighted to hear that we’ve been selected as one of the 7 participants of the study.  The rebate and technical assistance of this program is funded through the Proposition 84 Monterey Bay Regional LID Planning and Incentives Program grant.  Sherry Lee Bryan of Ecology Action has been instrumental in providing technical assistance.  Thanks Sherry!

Some of you may say, “Why worry about the small reduction in household water use when the largest consumer of water is electric utilities and agriculture?”  Well, if you’re looking at the aggregate data for the country and if you are in a position to do something about it then by all means please focus your efforts in those areas.  I am not in such position and as a homeowner living in an area where we rely on local watershed for our drinking water I’m doing my part to save water.

Curiosity tidbit:  Water is the 2nd largest chunk of spending by our city government (Santa Cruz).

Next month Jon Ramsey and his crew from AquaSoleil will be installing a green 4,995 gallon tank in the corner of our yard along with the agricultural grade pump. They’ll make the necessary connections to the plumbing and the system will be tested.  Then we wait for the rain. It won’t be until we get a good storm or two to fill the tank to see this system in action.  This could be as early as September (wishful thinking) or as late as November (more likely the case).

I will share the photos and notes of the system after it’s installed in July.


January 21, 2012

We’re finally having a good winter storm!  We’ve been having drier than normal weather since construction started last month and this was lucky for us.  Up until the arrival of the rain the crew was busy installing a perimeter french drain and ensuring drainage under the house.

As you’ve seen in the photos of earlier posting, excessive water can cause the wood to rot and cause structural problems as well as invite mold to grow.  To prevent water damage and keeping the house dry for comfort we have specified french drain and crawl space sealing.

French Drain
The perimeter french drain was dug down 18″-24″ deep along the perimeter of the house about 16″ away from the foundation.  Mirafi drainage fabric (filter fiber) is used to line the cavity and drainage pipes (perforated PVC) are placed.  Drainage rocks fill the cavity and topped off with soil.  So, when it rains the water will eventually find it’s way into the drainage pipe and the drainage pipe is sloped towards the back to fill the water garden by gravity.  The perimeter french drain helps prevent the water from pooling under the crawl space.

Digging along the perimeter of the house

Note that there are 2 pipes in the trench.  One of the pipe is perforated and will take in water — this is for the french drain.  The other one will be connected to the downspouts to route the water from the roof to the rain water harvesting tank at the corner of the property.  (By the way, the installation of the rainwater tank will be done as a community workshop coordinated through the local Resource Conservation District.  Stay tuned for that workshop in the late summer or early fall!)

Notice the drainage pipe is placed above mirafi fabric and gravel
French drain and rainwater harvesting pipe in the trench leading to back of the yard.

An interesting tidbit:  What’s the origin of the term, “French Drain?”  Well, I initially envisioned some clever drainage system in France.  It turns out the term is attributed to a lawyer named Henry French in Massachusetts who popularized the concept in his 1859 book, “Farm Drainage.”

Crawl Space Work
For a few days the crew got into their jump suits and crawled around to dig out drainage path under the house, install some pipes and sealing the dirt floor with plastic.  They had a cozy work space with lights and music under the floor.

You can see that there is a little carved out channel to direct the water beneath the plastic

Sump pump is installed under the house to pump out any water that pools under the plastic.  Note the electrical line coming out from under the plastic.  The sump pump will eventually be connected to an outlet.

This view is from the cutout in the kitchen floor looking down into the crawlspace

At each pier the plastic liner was taped to the concrete using Siga tape.

View of the sealed crawlspace

Rain Garden Pit
The water from the perimeter french drain as well as any overflow from the rainwater storage tank will go into the rain garden.  This was dug about 5′ deep.  The plastic “thing” (I don’t remember what it’s called) is a way to store larger volume of water than simply having drainage rocks covering the pit.

You can get a sense of the size of the pit with a really tall guy walking in it

When we get to the landscaping stage the area above this pit will have appropriate plants for rain garden.   For now it is covered up with soil and it looks like any other part of the yard.

Rain Garden pit is covered up

Other Work While Digging
Water line and sewage line from the street to the house were also replaced while all the digging was going on.  You just never know what you find when you dig.  The water line from the street to the house was a PEX pipe!  This is a flexible pipe that is used for indoor plumbing but not for external work.  The sewer line was made out of clay.

Fragment of old sewage pipe

Rain and Drain

“Talk to everyone and ask them what they know…” was one of the advice we received recently.  This paid off in our quest for water solution.  The water problems we are addressing, in order of priority, are:

  1. Reduce moisture in the crawlspace under the house.  Moisture/water is essential for mold growth and during the rainy season the mold spores are happily multiplying under the house.  Because the house is not tightly sealed the smell of mold is present in the house during the rainy season.  My mother told me I developed asthma as a toddler living in a moldy house.  So, dry crawlspace means less mold and healthier indoor air quality. 
  2. Keep rainwater away from the house.  Directing the water away from the house will help keep the crawlspace drier and keep the house structure drier.  On one of the photos we saw from the house inspection was signs of water on the wooden posts under the house.  We want to prevent rot and keep the structure healthy too.
  3. Recharge the groundwater on the property.  Sending it down the storm drain alleviates our problem at the house but it still may contribute to erosion and depending on what is carried by the water from our property (e.g. asphalt bits from the roof, residual pesticides on landscaping, etc.) it may contribute to water quality issues.

We know from talking to our neighbors that there is good chunk of clay under the topsoil that prevents water from draining nicely.  It will eventually drain, but this is very slow.  Our neighbors have multiple sump pumps to drain the excess rainwater on their property to the storm drain. 

Getting a soils report done is quite expensive so we followed up on an idea that was mentioned by a contractor who installs solar panel.  He said, “Why not go through the yellow pages under septic system installation and ask them if they’ve done vertical leech field for water drainage purpose around the westside?”  Hmm… interesting thought.  That would be great way to find out about the geology and soils condition.  We would not have thought about talking to the septic people since we’re connected to the city sewer, but the application makes sense.  So I flipped the yellow pages and rattled off the phone numbers while Kurt spoke with them.  We ended up having Darryl from Battle Mountain Excavation dig a monitoring hole using a hand auger and installing a 2 inch PVC pipe for monitoring.

So what are we monitoring?  Well, we learned that just because you hit sand below the clay, it doesn’t mean that the rain water will simply drain into the sand.  Apparently there could be different water dynamics going on at different levels.  One way to measure how quickly the layer below the clay absorbs water is to put in a monitoring hole using a PVC pipe that is perforated on the bottom then sealing the top with clay to isolate the water level activity happening at the lower level.

The drilling work done by Darryl and his crew was informative. Basically there is good topsoil for the first 16″ then there is dark clay, followed by lighter color clay and finally sand.

Cross section diagram of the monitoring hole

The pipe is capped at the top to prevent rain from getting in.  Periodically we will measure the water level beneath the clay layer by dropping a tape measure with a float at the end to read the depth.

Dark color clay like this is beneath the topsoil.  Goes down to about 43 inches.

Then it changes to lighter color clay and goes down until 8 feet.

So, if we determine that the water level below the clay has capacity to absorb water during/after storms then we’ll likely have a french drain or a swale created in the backyard for drainage.

Also, if we have to pump the rain water to the storm drain we found out that it’s not so bad.  We talked to Dave Reid, a fellow water enthusiast with geology background and learned that there is a public online application that map the storm drain flows.  We used this to find out where the storm water went.  Here’s the link to this GIS mapping tool – http://npdesgis.co.santa-cruz.ca.us/

Storm water from our area goes to Neary Lagoon, a wetland in middle of the city next to the water treatment facility.  This wetland is a habitat for various wildlife, including the fish, Sacramento suckers that graze the bottom like vacuum cleaners.  They suck up layer of algae, invertebrates and bacteria.

Diverting Rain Water

December 24, 2010
It’s rainy season here in Santa Cruz.  So far we’ve had 14 days of rain this month (December).  November had 9 days of rain and October had 6 days of rain.  Ever since we learned that there is evidence of high water pooled under the house (from home inspection we did during escrow) we’ve been thinking about mitigating the impact from the winter rain on the house.  Excessive moisture fuel mold growth and wet wood will compromise the integrity of the structure.  So, we want to divert the rain water away from the house.
A while ago we talked to Robert, prior owner of the house, and he mentioned that there is a drainage tube that was placed parallel between the house and the driveway to divert the pooled water in the back of the yard towards the street into the storm drain.  This drainage tube is now covered up in grass and hardly visible.  We don’t intend to use this if we can help it.  Why?  Because (a) Rainwater could be harvested and used to water the plants on the property; and (b) Large volume of rainwater discharging in to the storm drain cause problems such as erosion and degraded wildlife habitat.  Allow me to digress on this second point.  
Have you seen a label next to the storm drain?  It may say, “No Dumping Flows to Bay,” or a variation of this message.  This means that the liquid that goes into the storm drain does not get treated at sewage treatment plants.  The storm drain water simply goes into a local watershed, transporting whatever it picks up along the way to the stream, ocean, etc.  OK, that’s not big news and we’re not dumping automobile engine oil in the storm drain.  Still, there are indirect ways that we may be contributing to the water pollution.  Maybe it’s the fertilizer to keep the grass green or the pesticide used to kill weeds.  Perhaps it’s the bitumen or asphalt on our roof that is slowly degrading in the sun and transported by the rain.  We want to minimize these pollutants from getting into our watershed and also avoid erosion from high volume of storm water moving quickly through the system.  All right, enough of my rant about avoiding directing rain water into storm drain and back to the house…
We also talked to our neighbor about rain water and “flooding” in the backyard during storms.  In the past few years they have done a major renovation to their home by removing several feet of soil from their crawlspace and converting the crawlspace into a beautiful basement that opens out to the backyard.  During their project they found that the soil has high clay content that does not drain well and found the water table to be high.
Next, went on a quest for water table data.   First, we tried the water department with the city of Santa Cruz.  They pointed us to the public works department.  The people at the public works department was friendly and helpful, but they didn’t have water table data.  One of the engineers mentioned that ordering a soils report from a soils professional would be the way to get complete analysis and it would be very expensive.  A low cost alternative would be to simply dig a hole of 3-6 feet in the backyard and see if we hit water.  So that’s what we did.
About a month ago Kurt dug a hole of about 8 inches in diameter using a post hole digger — one in the back yard and one in the front yard to see if the water table is high as the rumor has it to be.  It was.  It was a clear day and the soil dug up was still moist from the rain over the weekend.  He stopped digging after 30 inches or so.  Observing that the dirt at the bottom was visible he walked away.  Then 30 minutes later he looked in the hole and saw 2 inches of standing water at the bottom! 
What to do with this?  We have a crawlspace that potentially floods.  The soil in our area has high clay content and does not drain well.  The water table is high in our area.  We want to avoid sending rain water down the storm drain. Hmm….
Since our first priority is to “protect the house” we took a temporary measure to divert the rainwater from the downspout away from the foundation of the house.  We will keep these downspout extension tubes in place until spring.
We plan to include a landscape designer as part of the overall design team so that rainwater harvesting system can be integrated into the overall design.  Right now we are thinking of putting rain pillows under the deck on the south side of the house.  Eventually the yard will be covered with mulch that will absorb rainwater and native plants that require little or no watering (once established).  The timing of actual implementation of the landscaping design will be after the house completion.
By the way, there is a great free resource for rainwater management for single family homes called, “Watershed Stewardship Toolkit,” prepared by Coastal Watershed Council.  It’s an easy to read document with specific examples for the things we are considering, such as rain pillows or cisterns, vegetated swales or rain garden, soil amendments and more.  This document is available from CWC’s stewardship page on their website.