Why harvest rainwater:
In the Southwest, to maximize life in a certain area of your home, you must first design for that area to hold the greatest amount of water possible. Passive rainwater harvesting uses land shaping, or earthworks, to slow and control storm water, and direct it into the ground instead of into the streets. Well-designed systems never hold water on the surface for very long. Water is directed to densely planted, thickly mulched basins that act as sponges to absorb moisture quickly. The earth then stores the water acting like a savings bank that plants draw from in times of drought. The approach to managing water also helps recharge our shallow aquifer. Once water is in the ground, it can no longer erode the soil and fill waterways with sediment. Furthermore, healthy soils filter out the pollutants that drain off of roads and parking lots so waterways stay cleaner.
We achieve these goals by assessing the site to find out where water is draining from and where it is going. Does water come from the neighbors roof or yard? Where does water drain off of the house? Where is the water going now and where do we want it to go? Once these questions have been answered we then create a plan to harvest the water. The way we do this is by using raised pathways and depressed planting basins. This is the simplest way to harvest rainwater. The pathways are raised and stay high and dry during rains, while the planting basins are filling up with water. We also use stream beds and channels to direct runoff from parking areas of rooftops directly into planting basins. On large sites we use swales to direct sheet flow run off into settlement basins or into other swales.
Once the passive system is designed we then move to Active Rainwater Harvesting. Active rainwater harvesting is directly capturing run off from the roof or pavement and direction it into cisterns to be stored and used for a later time.
You may ask yourself, “Why should I invest in harvesting rainwater in NM when it rains so little?”. It’s a very good question. In Santa Fe, NM we get an annual average of 14” of rain a year. On a 1,000 square foot house that equals 8,400 gallons of water that run off the roof a year. That’s a lot of water. Obviously there is no need to have a tank to hold that much water. The goal of rainwater harvesting should be to have enough storage capacity to span periods of drought. It’s like a savings account, you want to have enough money saved up to pay the bills when no money is coming in. We usually start with a 550 gallon tank. For a small garden that is enough water to span a 2 week period of drought.
Rainwater cisterns are made of molded black polyethylene plastic . They are sealed so that no light enters the water to grow algae, and no bugs can enter to breed. Each tank has an overflow as well as an outlet for hooking a hose up to. We can also install systems that feature a pressurized pump for on demand water. These can be used for spigots or irrigation in the garden. We can also attach a trellis to the tank and grow grapes on it.
Advantages of Rainwater Harvesting:
- Rainwater is a relatively clean and available resource
- It’s free from the sky.
- Collecting rainwater is sustainable and environmentally responsible.
- It conserves ground water.
- It results in less erosion and storm water problems.
- Rainwater is better for your plants than municipal or groundwater that is high in salts and chlorine.
- It uses simple technologies that are easy to maintain.
- Cost savings with rising water costs.
- It recharges our aquifer.