Another great set of questions I ran across that are very frequently asked:
How much rainwater falls on your roof? Each inch of rainfall drops 1,240 gallons on a 2000 square foot roof. To approximate the amount of rainwater falling on your roof, multiply the square footage of your roof footprint(including porches and garage) by .62 to get your gallons per inch of rain. Tip: if you don’t know the square footage of your roof footprint, substitute your house square footage.
How much rainwater can you collect from your roof? It depends mainly on the annual rainfall in your area, but also on the “runoff efficiency” of your roof. A conservative estimate would be 85% efficiency due to evaporation, splashing, and roof surface smoothness. So a realistic collection amount from that inch of water on a 2000 square foot roof is 1,054 gallons. Multiply the square footage of your roof by .527 to get a conservative estimate of your collection potential.
How can you use less water on your yard? Water used for foundation plantings and gardens can be cut in half by using drip irrigation and mulch instead of sprinklers or sprayers. St. Augustine turf needs about an inch of water a week to stay green. Several varieties of Bermuda need only half that amount. Buffalo grass needs almost no supplemental watering once established, but it needs a lot of sun. Consider replacing your sunnier areas of St. Augustine with Buffalo grass, and creating mulched areas in the shadiest spots planted with native or adapted low water use plants. You can probably reduce your turf water use by half or better.
Why does grass look so much greener after a rain? Rain clouds form in the sky when water vapor in the atmosphere cools and forms droplets. These droplets also contain dissolved nitrogen that comes from the air. (Nitrogen is the main active ingredient in commercial lawn fertilizer). Rainwater, whether it comes as rainfall or from a rainwater storage tank, greens up your grass with free, natural fertilizer. And you will be “greener” since this free fertilizer isn’t made from hydrocarbons.
How much water do you use in your house? Nationwide, we use about 150 gallons per day per person, which includes outdoor use. Indoors, we use about 70 gallons per day per person. Of that, less than 5% is used for drinking and cooking. Most is used for washing dishes and clothes, flushing toilets and bathing. It takes 2 gallons to brush your teeth, 2 to 7 gallons to flush a toilet, and 25 to 50 gallons to take a shower. If you have low-flow toilets and faucets, usage might drop to about 60 gallons per person. By using water-efficient appliances and water-conserving practices, you can achieve a daily per-person usage lower than 50 gallons per person.