05041 Rainwater Harvesting

Show the flow. Cycle it. Celebrate it. Know it. And as you do, show others the way. — Brad Lancaster

Rainwater harvesting involves catching, conservation, and responsible use of the free gift of rainwater.

In most urban areas, municipal authorities consider rainwater to be a nuisance. They channel it into underground storm sewers and discharge it as quickly as possible into the watershed, together with the load of toxic chemicals that it picks up during its journey.

If you are a renter or resident in a college dormitory, you have a limited ability to take direct advantage of rainwater. You may be able to catch some rainwater in totes or other containers and use it to water plants or even flush toilets. Your real influence however will be in the area of invisible structures.

If you live on campus, your campus has extensive, and expensive, systems to funnel rainwater into storm sewers. Campuses would benefit from using rainwater harvesting to divert rainwater from storm sewers into their landscapes. Every gallon of rainwater used to water the school landscape is a gallon that the school does not have to buy from its water utility and thus a price it does not have to collect from its students.

If you are not a student, and if you rent, work with friends and family and neighbors to develop more rational water use policies for your watershed. Speak with your landlord about the advantages of rainwater harvesting.

If you own a condominium, you can work with your condo association to harvest rainwater and put it to use to benefit the association.

If you own a house with a yard, there is a considerable amount of work you can do to harvest rainwater.

There are two primary ways of harvesting rainwater — earth works and active systems.

Earth works refers to swales, berms, spill-a-ways, terraces, and other systems that passively channel rainwater into a landscape. An active system collects rain from rooftops and channels it via gutters into storage containers for use later. Active systems cost more than passive. Passive systems can be done simply, with a shovel and hard work. As with anything, you must first study the lay of your land. Get your umbrella and wander around when it rains and see where the rain goes naturally. This will help you to plan how to develop your swales, berms, and retention basins.

The potential of rainwater harvest should not be dismissed as negligible.

One inch of rain equals 633 gallons per 1,000 square feet (2.54 centimeters of rain equals 2,396 liters per 93 square meters of roof).

12 inches of rain equals 7,480 gallons per 1,000 square feet (30.5 centimeters equals 28,315 per 93 square meters of roof).

36 inches of rain equals 22,400 gallons of water, per 1,000 square feet. (.9 meters of rain equals 84,793 liters per 93 square meters of roof)

Google says that the average size of a college campus in the United States is 440 acres (178 hectares), with each acre equal to 43,560 sq feet (4,047 square meters).

For every acre (.4 hectare) on a college campus, and for every foot (30.5 centimeters) of annual rainfall, the potential rainwater harvest is 325,829 gallons (1,233,397 liters). That amount of rain would be representative for a college in a desert area.

For an area with more rainfall, say 36 inches or 3 feet (.9 meters), the amount of rainwater per acre is 977,476 gallons (3,700,149 liters).

If we think about our “average campus” of 440 acres (178 hectares), if it’s in a desert where its only getting 12 inches (30.5 centimeters) of rain per year, that amounts to 143,364,672 gallons (542,694,350 liters).

In a better watered state, with say 36 inches (.9 meter)of rain, we’re talking 430,094,016 gallons (1.6 billion liters). Yes, that’s correct, four hundred thirty MILLION ninety-four THOUSAND sixteen gallons on 440 acres in a 36-inch rain year.

Whether you are a college student or not . . . the point here is to stop seeing rainwater as a nuisance and an expense, and start thinking about it as this incredible free gift that the hydrological cycle gives us every year.

The best introduction to rainwater harvesting, at whatever scale you contemplate, is Rainwater Harvesting for Drylands and Beyond, whose website is http://www.rainwaterharvesting.com/.

Study these books to learn about the opportunities and options of rainwater harvesting.

As you develop your design for your life, look for opportunities to integrate rainwater harvesting and to encourage invisible structures such as schools, businesses, houses of worship, and governments to collect and responsibly use the water before sending it further downstream.