July 2014

Rainwater: Good Water with Good Uses


Doug Pushard


For millennia, humans used rainwater for a variety of purposes, including drinking, washing and irrigation. Yet these days, rainwater can be highly polluted and not suitable for use. Still, it is one of our purest sources for water, and with the right treatment it has many uses.


When rain falls onto a polluted roadway or roof it becomes contaminated with everything it touches. But before it hits the ground, rainwater is relatively pure. Compared to well water (i.e., groundwater), which is typically very high in minerals, rainwater is cleaner and easier to purify. And unlike the water in lakes and streams (i.e., surface water), rainwater contains no pharmaceuticals, minerals or pollutants.


We drink, flush, bathe and irrigate with water from wells, streams and lakes and can do the same with rainwater. The planned use of the rainwater determines the type of treatment necessary.


If you are using rainwater in a drip-irrigation system, very little treatment is needed—just simple gutter or canale screens and then a 200-mesh filter. The filter prevents the sand and particulates from clogging up the drip heads. Rain is nature’s way of watering plants, and your garden will thrive on it. Unlike typical municipal water and well water, rainwater contains no salts or minerals. In fact, rain dilutes salts in our soils that can, over the long term, be very harmful for landscaping.


Much finer filtration is required to make rainwater suitable for drinking. Along with the canale or downspout screens, a 25-micron filter followed by a five- or one-micron filter is required. Like lake, stream and pond water, rainwater will contain bacteria. City water is treated with chlorine to address this problem. Small municipal and residential systems typically use either ultraviolet light (UV), ozone or both to deal with this issue. These two technologies are well known, used around the world and not highly expensive.


Rainwater can be used for irrigation without much processing and can be made potable with appropriate, widely used technology. In addition, there are other uses for rainwater that can have a meaningful impact on our water use that are worth considering.


Toilet flushing is one such example. Flushing human waste down the toilet is the top use of clean drinking water in most households. Why use a limited resource for something that literally goes down the drain? Clothes washing is another great use for rainwater. The water used for flushing toilets and washing clothes doesn’t need to be treated to drinking water standards. Recently released plumbing codes recognize that alternative water sources such as rainwater can be used in both toilets and washing machines with the proper signage and precautions. By implementing these simple applications, a typical household could drop its potable water usage by more than a third.


Such savings would greatly reduce your monthly water bill and help in a variety of other ways. One big, indirect cost-saver would be reducing the need for new water treatment plants. In the Santa Fe area, the recently constructed Buckman Regional Water Treatment Plant cost in excess of $220 million, and expanding this plant or building another one is likely to cost much more. Delaying this forever, or for as long as possible, would be in all our best interests.


Additionally, by cutting down on our potable water use we reduce the pollution from transporting and treating water. It is estimated that conveying, treating and delivering potable water consumes about 15 to 19 percent of the nation’s power. The Buckman Direct Diversion project has installed solar panels to reduce this reliance on fossil fuels, but it is still one of the major costs to this utility.


Rainwater is free, and although climate changes and changing weather patterns may affect its regularity and intensity, it should be part of the solution to our water future. It is cleaner than most other sources, and its use is only limited by our imagination.



Doug Pushard, founder of HarvestH2o.com, is a member of the city of Santa Fe Water Conservation Committee. He designs and installs active and passive rainwater systems in northern New Mexico. doug@harvesth2o.com




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