Sunday, March 1, 2009

Rain Water Capture

How great would it be if we could capture all the rain that falls on our house and driveway and use it to sprinkle our yards? Or flush our toilets? I started this project a few months ago...boy did I have a lot to learn.

Rainwater capture for most of us means we use gravity to put the water in storage. That means we can't really capture the water from our driveway or other concrete areas without holes and pumps. There is some cool stuff you can do if doing new construction, but my project was for my existing home.

First, there are calculators out there that you enter the square foot of your roof, estimate how much you can capture of that depending on gutters, roof material etc. If your house is guttered you will generally capture about 70%. Then you get the monthly rain estimate in inches for our area. Multiply the two and you know how many gallons in theory you can get from your roof based on past rainfall. Seems simple no?

After I figure out how much water I can get from my roof I need to figure out how much I use. That means I need to get to my water meter, run my sprinklers and figure out how much I am using. It turned out I used 9000 gallons each time I ran the sprinklers! So I just figured I would need a lot of storage.

Some of you have seen, or even own a rain barrel or two. You basically stick the thing under your downspout. Unfortunately, the first time you calculate your sprinkler's water use for just a minute, you will realize that these are grossly inadequate in size. My smallest sprinkler zone, about six heads, uses 24 gallons a minute! That's two minutes from a 55 gallon drum! These barrels are best used to water shrubs or a small garden in the immediately adjacent area.

So, it turns out you need some pretty big storage. In our neighborhood there are people with large above ground tanks either capturing rain water or connected to a shallow water well. They are large and typically eyesores but they hold between 2-3000 gallons. Tanks of that size cost around a dollar a gallon to buy and estimate another two dollars per gallon to install, connect pumps etc. So a 3000 gallon tank would run me $9000. Every time I filled it with rainwater and used it I would save myself $11.10. Or, I would need to fill and empty it 811 times to pay it off.

However I would need three just to cover one sprinkler run! You also begin to realize that your figures are based on average rainfall. I was sprinkling once a week but what if it didn't rain every week? How could I be sure my tanks would be full? And if it was raining weekly I wouldn't need to sprinkle! Then my head began to hurt. If it rains I don't need to sprinkle and when it doesn't rain I need to sprinkle...hmmmm. I would really need even more storage...or something.

That something was I was using too much water to sprinkle! My roof and huge tanks weren't going to get the job done. Now I have a large yard but I am just talking about how many gallons per square foot, per week I used. If I couldn't reduce it, rain water capture wouldn't work.

Bottom Line- The more water you can store the more likely you are to have water when you need it but you may have to think of your system as purely supplemental. You also have to consider your ROI is going to take a few years and the aesthetics of above ground tanks aren't good. Most importantly, you have to change your sprinkling habits and water use, then and only then can rainwater capture provide significant help. I will be posting my success reducing my sprinkler's water use...that project was a lot more fruitful.

No comments:

Post a Comment