By Curtis Millsap – I’ve learned a little about water in the past year and a half since moving to New Mexico, and the last issue of COUNTRYSIDE inspired me to pass on a little of the knowledge I’ve gleaned about off grid water systems. The area we live in is not conducive to wells, being 8,500 feet above sea level on a piedmont overlooking the Rio Grande Gorge. Instead, there are two commonly used options: rainwater catchment and ditch water.
Rain water harvesting off roofs is moderately more complicated than the second option, but probably yields higher quality water. I don’t personally have experience with this, but the basic mechanisms are simple for this off grid water system.
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1. A coated steel roof is the roof of choice, because there is no contaminating runoff from the baked-on finish.
2. Most systems have some sort of device in the gutters to ensure that the dust and leaves from the roof don’t end up in the cistern. In some houses this is a valve which allows the first few gallons of water to run out on to the ground, and then diverts the water to the cistern. Other systems have a baffle system which catches the majority of the silt and organic matter. Still others just have a little window screen in a large funnel. The purpose is to try to ensure relatively clean water in the cistern.
3. The cistern (many are not technically cisterns since cisterns are buried) is a large tank. In this area most people who are using rainwater exclusively have at least a 4,000 gallon cistern, but a few of my acquaintances have run dry this year due to the drought we are experiencing. Most agree that if they had 6,000 gallon tanks they would still have water. I imagine you could have a much smaller cistern if you lived in a more moist climate than northern New Mexico. One important thing to consider is how much water you use per week, and plan accordingly; in New Mexico that means having at least a three month reserve. Cisterns can be made of many materials, given that it is waterproof, tasteless, and safe for drinking water. Many cisterns are a food grade plastic, which is fairly expensive (I think around 60 cents a gallon last time I checked). Others are concrete, either custom dug and poured on site or a box similar to a septic vault poured off site. Concrete has the advantage of being cheaper and potentially homemade, but must be coated with some sort of sealer on the inside and is more difficult to install and more likely to develop leaks. I am amazed at the amount of water which can be gathered off a roof, even in such an arid environment. Most of the people we know have full tanks most of the year, and get about a thousand gallons per inch of rain from an average-sized roof.
The second off grid water system for water procurement in our area is fill from a stream or irrigation ditch. The water comes out of a mountain valley which is uninhabited (by people), and flows into a ditch which runs down the hill and around my yard. The Acequia, as it is known in Spanish, is communally owned and maintained, and we have rights to a certain share of the water which comes down the ditch. Once a week we stick a 1-1/2” pipe into the ditch and siphon water to our cistern, which is actually two concrete vaults joined by a pipe that runs to my basement.
Whichever way you choose to fill your cistern, the next steps are common to both rainwater catchment and ditchwater. A water pump like a shallow well pump or irrigation pump is connected to the pipe coming from the cistern, and then there is a pressure tank, which allows the water to accumulate a pressure reserve, just like in a well. From here it goes to a filter and purifier. The most common filters up here are PURA, a brand that produces three-step inline filters, going from 20 microns to five microns to a U.V. lamp. The first two chambers remove all the sediment, and the final chamber kills any bacteria or viruses in the water. The PURA setup for a whole house (eight gallons a minute maximum) runs about $700 dollars new, and the U.V. unit alone costs $300 (Ed Note: Costs in 2003). Some people choose to have a smaller unit under the sink, which reduces the cost, but only allows you to drink water from the kitchen sink. There are other equivalent units out there, but I know this one works. The key in U.V. purification is that the water must be clear, with no sediment. Any sediment will block the U.V. light and allow some bacteria or viruses to pass through unharmed. The wonderful thing about U.V. is it leaves no residue, and so the water tastes wonderful, and has no chlorine and other chemicals added to it. To increase the life of your filters and reduce silt in the water, always allow the water to settle overnight after filling. We’ve had to learn this lesson the hard way, replacing sediment filters once a week for a while; at $15 dollars a filter, this gets expensive quick. We also clean out our cistern once a year, and this makes a big difference in the flavor and quality of the water, not to mention filter life.
When you have to gather water yourself, you become much are of recycling water at home. We have a conventional house, with flush toilets and a septic system, and my family of four uses close to 1,500 gallons of water a week. I have several friends who use less than 300 gallons, and still manage to take care of a small garden and some trees. The key to reducing water use is to reuse as much as you can, and be conscientious every time you turn on the faucet. We re-use water in several ways.
I made a DIY grey water system that collects the water from the washing machine and kitchen sink in a sump basin in the basement (a sump basin is basically a plastic 55-gallon drum with a movable lid). A sump pump then pumps this water outside into two 55-gallon drums which are connected to each other and a spigot. The drums sit about four feet off the ground on a wooden stand. We use this to water the garden, and while it smells horrible with all the organic matter in it, I think it is great for the garden. As it is, we do not have any kind of filer on it, so I am hesitant to run it through my drip system, but we do a lot of our watering with this water. We still have to augment this with water from the spigot on the house, but I hope to hook up the shower to the grey water system someday, and I think then we will have enough to do all our watering with grey water. One thing to keep in mind when setting up a DIY grey water system that keeps the water outside, is to make a plan for cold weather. My system has valves at the junctions so when winter rolls around I can divert the water back into the septic tank. Our grey water system is pretty basic compared to many around my area; if you are interested, look for information on “earthship homes,” which are totally independent and often re-use water at least once if not more.
My wife and I keep a plastic bowl in our bathroom sink basin, which catches all the water from brushing our teeth and washing our hands. We use this water to either flush the toilet or water some houseplants. An added benefit of this method is it heightens your awareness of how much water you are using (or wasting if you leave the water on while brushing your teeth).
We also sometimes plug up the tub while taking a shower and dip that water out in a pitcher to water plants.
Planting a garden at the bottom of a slope is an old dry-farming technique, and it works great, effectively doubling or tripling the rainfall on a plot of land.
Hope this is of some help with considering off grid water systems, and if anyone has any questions or suggestions, I would love to hear from them. I strongly recommend collecting water and being more in tune with our most valuable resource; it’s very rewarding to free yourself (at least somewhat) from another utility.
Originally published in 2002