Brad Lancaster, author, Rainwater Harvesting for Drylands and Beyond
Water from your air-conditioner? That's just one unconventional source of moisture you can tap for your garden, according to author Brad Lancaster. He lives on an urban lot in Tucson, Arizona and catches and reuses almost all of the rainwater that falls on his property. On Saturday, he'll visit Las Vegas for a one-day seminar on rainwater collection. He joins us to discuss some techniques for maximizing moisture in the desert.
Q: We only get about four inches of rainwater a year in Las Vegas. If someone were to harvest that with a collection system, how much water would that be?
It can be substantial. For just one inch of rain falling on a one-acre site, that would be over 27,000 gallons a year – again, that’s just for one inch of rain falling on that acre. So it can be good. And especially if you are capturing water not only from your roof, but from your other hardscapes like your driveways, patios and sidewalks. If you direct that water not to the street, but instead direct it to your landscape, you can triple the available rainfall in those landscaped areas, so increasing your available rainfall from 4 inches to 12 inches a year.
Q: So when we talk about a water collection system, what does that look like?
It can be a number of things. Typically people think of tanks so there being a gutter on the roof that directs water to a downspout and then a tank. And that is definitely one strategy, but that’s not where I recommend people begin. Instead, I recommend people begin by just changing the surface of their landscape so instead of being hill-like that drains top soil and water, instead be bowl-like, which harvests and infiltrates water, and also collects biomass and increases soil fertility. Basically what that would look like, is you still have your roof draining water to the landscape with a gutter or without a gutter. Then you will have this bowl-like or depressed topography in your yard that pools the water and then rapidly infiltrates it so you have no puddles and no mosquito issues and the soil then becomes your tank, so you don’t have to buy a tank. Thus this costs no more than the price of the shovel if you do the work, and that way you get the water back out is by planting pumps. You use the vegetation and the landscape draws it up through the roots, and you can use the water in the form of shade, wildlife habitats, beauty food production and so on .
Q. This is water that doesn’t end up in Lake Mead ultimately, so doesn’t that impact local water supply?
This harvesting of rain water impacts in a positive way, because while you do have water going to Lake Mead, the water just drains off. You’re losing the bulk of that water to evaporation, not only as that water is travelling to Lake Mead, but once it gets to Lake Mead. We’re in a dry land environment where potential water loss to evaporation dramatically exceeds water gain to precipitation. In this environment, I feel what is very key is that we do anything and everything we can to reduce water loss to evaporation, and if we store water on the surface behind a dam in a reservoir for instance. Or we drain the water over the surface through surface drains over great distances, that dramatically increases loss by evaporation. So this way we get the water into the soil, beneath the soil, beneath the mulch, so it lasts longer into the dry spell.