Rainwater Harvesting

I mentioned in earlier posts that we’re going to be harvesting our rainwater.  I wanted to do a small deep dive into this subject because it’s such a new Green concept.  Our contractor is [NAME OF CONTRACTOR DELETED ON 5/18/09] – they’re the premier rainwater harvesting company in North Texas.

I will touch on a couple of topics:

How much water do we think we can get?  We’re collecting from our entire roof, which is roughly 2900 square feet.  The accepted calculation is that 1 inch of rain on every 1000 square feet of roof yields 600 gallons.  So for every 1 inch of rain, we’ll collect about 1740 gallons.  We are installing two 2500 gallon cisterns, so a good 3 inches of rain and we’ll be full!

How much does it cost?  The quote we got from our rainwater harvesting contractor was about $8800, but keep in mind that includes not only the downspouts, plumbing and cisterns, but also a filter/purification system that will enable us to use the rainwater in our washing machine, too.  We’re paying for gutters separately.

How much will we save?  Our former yard was almost entirely Saint Augustine grass.  We were watering every second day during the summer and at least twice a week during the winter.  Our water bills were anywhere from $200-$300/month.  We expect to save anywhere between $100-$200/month between having a drought-friendly landscape and using rainwater.  With a fairly conservative guess of $150/month, the rainwater harvesting system will be paid off in about 5 (or less) years.  Not a bad Green investment!

How is it put together?  Basically the gutters are installed first.  Then our contractor places the 4″ downspouts.  The downspouts run from the roofline, into the ground, across the property and up into the cisterns.  As long as the cisterns are below the roofline, gravity will feed the water into the cisterns.  Of concern with these systems are leaves and other roof debris.  We’re using a foam insert in our gutters – the idea being that the water soaks into the gutter while the leaves, etc stay on top and get washed off.  There is a filter into the cistern, and another going out of the cistern.  There is a pump that we’re installing in our crawlspace that feeds both the irrigation system and the washing machine.  Before the water goes into the washing machine, it goes through a very fine filter and then through an ultraviolet purifier.  If the cistern gets too low, a valve opens to fill the cistern with city water.  Our washing machine will be set up to be able to switch between cistern and city water…so we’re not stuck without the ability to wash clothes!  The cisterns also have an overflow into the landscape in the event we get too much rain and the cisterns are full.

Aesthetics.  Our cisterns are being installed above ground.  Obviously having them installed below ground would solve the aesthetics problem.  However, in our installation we have a side of the house that is fully utility – it will house the two cisterns, two air conditioning units and the electrical box.  It will be fenced in and hidden from the entertainment portions of the house and the neighbors.  So, for us there’s no aesthetics issue.  There is a house outside of Dallas that has a 10,000 gallon cistern in the backyard.  Some designers see it as a Green architectural design feature while others have criticized it as too much exposed utility.  Decide for yourself here:

We’re told that maintenance on the system is infrequent and simple.  Does anyone with a rainwater harvesting system agree or disagree?