Monday, January 11, 2010

Rainwater Harvesting

Getting Water From Raw Land

Tammy and I bought our property in the Texas hill country four years ago, and at that time the land was completely pristine, undeveloped, and untouched. It’s primary use for the previous 100 years had been cattle grazing and deer hunting.
There were no roads, no pathways, no electricity, no water well, no structures of any type… nothing but what nature put there – tabula rasa.

Water: Modern Conventional Wisdom vs Ancient Wisdom

Conventional wisdom says when you buy a piece of raw land the first thing you do is run electric service and drill a well. And that was our plan, until we attended a presentation on rainwater harvesting at a local nature center. I was amazed to learn that every drawback to well drilling simply did not exist with rainwater harvesting. It sounded too good to be true. The more research we did, the more we became convinced to use this method on our land.

Rainwater Harvesting Meets Our Irrigation Needs

Since we don’t live on the property, and have no house or other structure, the first requirement for water was for irrigation. Approximately 500 feet south of our future home site we wanted to plant a grove of fruit trees and establish a ¼-acre garden. This project provides an excellent study on the pros and cons of the two possible ways for us to provide irrigation water to this site: water well or rainwater harvesting.

click "pros and cons" table to see image full size

Rainwater is a great option when a well just isnt going to work.
well water vs rainwater harvesting

Drilling a water well would have cost us between $12,500 ~ $25,900 and would have been guaranteed to raise our property taxes. Building a rainwater harvesting system cost us $2,300. A water well requires installation and maintenance by a professional water well drilling company. A rainwater harvesting system can be constructed from parts readily available at hardware store/lumber yards, and if you can glue PVC pipe together and nail boards together - you can construct and maintain it yourself.

Here is a photo of the rainwater harvesting system nearing completion during the summer of 2009:

rainbarn, a pole barn for capturing rainwater.
rainwater harvesting system, pole barn to capture water
The system is comprised of a 3,000-gallon poly tank, a simple shed-type structure, a 18’x20’ corrugated, galvanized metal roof (set on a shallow angle) which creates a 330-square-foot rainwater catchment area. This system captures approximately 200 gallons of water from 1 inch of rain. Since this area receives average annual rainfall of 33 inches, this system will refill itself twice a year.

I constructed this “rain barn” during one of the most severe droughts in the state of Texas in many years. Contrary to what most people seem to think; a “drought” does not mean you receive no rain – it means you receive less than historic averages predict. This system went online in late June and was filled to capacity within 3-1/2 months... during a drought.

Since our land is a set on rolling hills, we utilized this feature and placed the rain barn at a slightly higher elevation than the area we wished to irrigate. The water is gravity fed into irrigation lines. The tank outlet is a 2” ball valve. This is reduced down to ½” PVC field lines. When you factor in the force of gravity with the water trying to move out of the tank and downhill, and the water’s aperture being reduced by a factor of 4 (going from a 2” opening down to ½” pipe) we are seeing about 10 PSI at the point of irrigation.

We use DIG brand battery powered timers/solenoid valves (water hose timers) to supply a drip system for a grove of newly planted fruit trees.

Since this water is used for irrigation only (it's not potable) it does not have to be filtered and sterilized before use, however the system has 3 levels of filtration for water before it enters the storage tank. Any biologcal material entering the tank will render the water putrid and possibly clog field lines and solenoid valves downstream of the tank itself. The first system is a leaf screen on the gutter:
gutter screens
gutter screens

This keeps leaves, acorns, large insects, and small sticks and other tree debris out of the system. The downspout (inside the gutter) is proteced with an even smaller diameter screen to catch anything that makes it past this leaf guard. The second level of filtering is known as a "roof washer". Essentially, this is a short, vertical section of 3" PVC that captures the first 10-gallons of water from a rainfall. Once this section is filled, all water after that flows into the tank. Diverting this first 10-gallons allows any dust, dirt, silt, or particulate matter to sink to the bottom of the "roof washer" and not enter the storage tank. This section of pipe has a removable cap, and we simply drain this water after every rainstorm. The last level of filtration is a sock filter installed on the tank inlet. This catches anything that manages to get past the leaf guard, downspout screen, and the roof washer.

Rainwater Harvesting is more Sustainable to the environment

One of the biggest issues in the Hill Country these days is the impact of development, and the amount of water being pulled up from the central Texas aquifers. This type of system draws no water from the local aquifers. We simply capture a tiny fraction of the total rainfall that lands on our property, and we store it.

The system is equipped with a simple overflow mechanism that diverts any additional water (once the 3,000 gallon tank is full). This overflow is run down a 30' section of perforated drain tubing and into a natural waterflow channel near the rain barn. From there, this channel flows into a 1/4 acre earthen tank, that was in place when we bought the land.