Rainwater Collection System

Rainwater Collection System
Water is a precious resource that we quite often take for granted. Like most everyone else, we had not taken it into consideration until we started planning the house. Over the last year we have kept track of how many gallons of water we use per year in our present home, and through a conscious effort I am happy to report that we only used 5,500 gallons of water. That’s about 7.5 gallons of water per day per person. According to the Texas Guide to Rainwater Harvesting, conservative households typically consume anywhere from 35 to 55 gallons per day. That seems like a lot to me, but I guess if you live in an arid region where you are watering lawns everyday that might be right. During the year that we kept statistics, I only watered our garden a couple of times and never watered our lawn.

Our plan is to use rainwater as our primary supply of domestic water and use the well water as backup. Through proper filtering, rainwater is superior to well water. But we also realize that there will be dry periods in which well water may be necessary. Well water will always be used for outside purposes such as watering the garden, providing water for livestock, etc.

One of the first projects that will be completed this year is the rainwater catchment system. If you recall, back in September a 2,440 gallon cistern was installed underground. Since the roof took until December to be completed, I was not able to build the system before winter set in. This has also given me time to think things through. (You may want to check out Ole’s web site for some great information on how his system is set up. Our system will be modeled after his to some degree. You may also want to check out the Texas Guide to Rainwater Harvesting.)

With our system, it was imperative that the main tank be stored underground to prevent the tank from freezing up in the winter. In warmer climates, you can leave the tank above ground if you choose. It’s easier to design an overflow system when the tank is above ground. I wrestled with this concept for a while. I did not want the main storage tank to overflow and flood the area adjacent to the tank. There would be risk of dirty water backflowing into the tank and that would not be a good thing. Summer thunderstorms have a tendency to drop inches of rain in short duration, so control is a must.
Click on image for larger view

I also had to figure out a roof washer system to take the initial rainwater and divert any dirt that might have collected on the roof. I initially thought of using a long 8″ PVC pipe and letting the sediment settle down at the bottom, while cleaner water would be routed from the top of the tube. This would work, but I still had no way of controlling an overflow situation down at the underground tank.

The solution to this is to use a 500 gallon holding tank to be used during the warmer months. This way I can control the flow into the main storage tank by using a valve. If the cistern is almost full, I will shut off the pipe feeding the cistern and control the flow manually. If the cistern is almost empty, I’ll keep the valve open and allow anything over the first 100 gallons of rainwater to flow into the cistern. The initial 100 gallons will be held in the holding tank and allowed to gradually seep out of the bottom drain.

Having almost 3,000 gallons of storage should give us plenty of storage for our normal consumption.