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Rainwater Collection

© Max Dalrymple

I mentioned last time there are 1500 square feet in the average Albuquerque house. Because of eves you'll have more area if you cover your house with a sloped roof. The southwestern roof is flat, however, and it is about the same size as the floor beneath it. 1500 square feet is probably a good estimate for the size of the average southwestern style roof.

We talked last week of accepting as a goal a much stronger standard than that of the City of Albuquerque's Xeriscape(TM) program. Specifically, instead of limiting only the six high water use ground covers or grasses the City limits, I am planning on limiting all of my high water use plants to about 20% of the total landscaped area. In the beginning that "high water plants" area equals about 570 square feet, although I am also planning on two pecans which will eventually grow large enough to shade the western and eastern sides of my house.

The pecan is a large tree and it will eventually take up much more water than the other high water use plants in my plan. To begin with, though, the pecans won't be much bigger than the other trees and will probably require a similar amount of water, perhaps about 10 gallons of water every 7 to 10 days that they're in leaf the first year. I'm going to plan for small pecan trees, with the knowledge that I'll have greater water needs and less water coming from my roof in a decade or so because of those pecans, which will be larger and which will be covering parts of the roof.

Total precipitation in this area is about 14" a year, with half of that falling in our summer monsoon months of July and August. According to the wet-climate rain collection web site you'll find here, one inch of water falling on 1 square foot surface similar to that of the southwestern roof produces .62 gallons. That's about 930 gallons of water a year from my roof, with nearly half that, or 465 gallons of water, falling in July and August.

Three Methods of Rainwater Conservation

There are at least three ways that rainwater can be conserved. One of them is to use a lot of compost and other organic matter around the trees and other high water use plants, then to drain the roof water directly into the compost. Organic matter absorbs moisture and holds the water in the soil for the plants to use when they need it.