Water security

Major update July 27, 2009

You might have read about California’s “water war” gearing back up. California has had water issues historically since the West Coast first started to get seriously developed, but many voices are now pointing to water as the next precious natural resource over which *real* wars will be fought.

Related, water rights have also been an ongoing concern for those requiring significant amounts for irrigation or ranches.
One solution that skirts the legality issues (sometimes) of water rights is roofwater harvesting. My plan is to stem the rain flow from our gutters to a new pond we’ll dig below our current vegetable garden and “food forest” (more on that later in a permaculture post).

Using a solar pump, we’ll bring the water up from the pond to a simple sand filter, then to an underground cistern. Our existing diffuser we already have buried in the backyard will become moot. Bummer. Wish my awareness of water issues had been higher five years ago when we installed the diffuser.

We’ll add a manual diverter between the pond and the sand filter to help keep the cistern water clean in case of a natural emergency (e.g. volcano erupts and we don’t want the ash clogging the filter).

Why an underground cistern? I don’t want anything exterior to the house that screams “We have extra water!”. Because the pond is so far away from the house, it should not attract that much attention. And even then, most folks will think of it as just a pond, not a large holding tank for usable water.

After collecting roof rainwater and having our county folks test it for total coliform counts, copper counts, etc, I know how extensive of a sand filter I need to build. I’ve now got sub-contractors putting together bids now for a 5000 gallon cistern system; our monthly water usage between the house and the gardens is ~ 4800.

So we’ll have one month’s water supply running at normal speed; much longer if we pay attention and ration this precious resource wisely. My goal is to have this complete within the next month or so. We’ll use the cistern water regularly for our garden irrigation, offsetting our water bill and allowing for fresh water to be reclaimed at each new rain.

Can this water be made potable? You bet. A nifty little product called Aerobic K-07 does the trick through hyper-oxygenation. Google it; lots of backpacking/camping gear retailers and websites sell it.

Here’s the rule of thumb to guesstimate how much water you could harvest annually: CATCHMENT AREA (in square feet) multiplied by the AVERAGE ANNUAL RAINFALL (in feet) multiplied by 7.48 (to convert cubic feet to gallons) equals the TOTAL RAINWATER FALLING ON THAT CATCHMENT IN AN AVERAGE YEAR.

So that is CATCHMENT AREA (ft2) x RAINFALL (ft) x 7.48 gal/ft3 = TOTAL AVAILABLE RAINWATER (gal/year). For me, that translates into 695,640 gallons annually.

Interested in learning more about harvesting your own roof runoff? This PDF is viewed as the Bible of rainwater harvesting. Don’t let the “Texas Manual” title throw you off. It is definitely applicable to all areas of the US.

Related side note: using the rule of thumb keeping one gallon of water per person, per day, on hand for emergencies, we’ve also got one month’s water supply stored in jugs. Be sure you don’t store your water jugs on a concrete floor; a chemical reaction occurs over time which fouls the water.