SATURDAY, FEB 21, 2015

Rainwater Catchment

How to harvest scarcity



TUCSON (A-P) — First, by catchment is meant catch and store, as distinct from divert or "harvest." Rainwater diversion directs runoff to favored areas such as around fruit trees. Diverting water after it has hit the ground is child's play, possibly involving mud, and children can figure out how to divert water. Catching and storing rainwater until it is needed for irrigation, or other uses, involves technology, math, building stuff, and so is best dealt with by adults, but the principles are simple and can be covered in a few to-the-point web pages. You don't need to wade through a three volume tome or attend one or more workshops at $700 a pop. For in-depth learning, for a work worth wading through, consider Rainwater Harvesting for Agriculture in the Dry Areas; by Theib Y. Oweis, Dieter Prinz, and Ahmed Y. Hachum, or read on.

Gravity is your friend. Catch water using gutters under eaves before it gets to the ground. Most gutters are connected to a simple downspout directing the water to the ground. This misses the important point concerning friends and leads to water diversion. To catch water for storage, think gutter empties rainwater into a vertical pipe. The closed pipe can then go underground to the edge of a water storage tank, go up a vertical pipe, elbow over, and go into the tank provided the end of the pipe is lower than where the water goes in. Water from gutters need not flow to a nearby tank and then into the top of it. A closed piping system can bring the water to the tank or tanks which need not be near the gutters. Multiple gutters can feed downpipes connected to a larger underground pipe taking water from all roofs in an area.

A 3 inch PVC thin wall irrigation pipe makes for a vertical down tube that fits over the gutter's short metal downspout. The downpipe furthest from the tank connects to a 3 inch PVC thin wall irrigation pipe perhaps going underground. If another downpipe ties in, transition to 4" PVC thin wall irrigation pipe. Multiple downspouts can tee into this pipe. Outside next to the tank, put a tee on the end pointing up with a short section of pipe with a cap pointing down to catch sediment and allow for a small solar pump to empty the pipe after a rain. The pipe coming up elbows into the above ground tank whose top is lower than the gutters. Gravity does all the work of filling the tank which has an overflow outlet that could fill another tank and so on. The tank could be uphill from the house, only the top needs to be lower than the gutters.

One way to get water out of an above ground tank is to put a hole in the bottom that doesn't leak that goes to a faucet. It is also possible to siphon the water out with one or more faucets lower than the water in the tank. If gravity fails, a small solar pump can pump water when the sun shines into a high enough small tank from which water can flow as needed by gravity. Such a gravity fed system is a low pressure system. Figure 0.43 psi/ft, so if water is 5 feet above outlet, water at outlet is 2.15 psi (pounds/ Irrigation using standard and expensive drip irrigation tech will not work as it assumes a high pressure water source (well or city water). The good news is that 1/4 inch drip hose stuck into irrigation line does work. For more water to a plant stick more drip hose in. The irrigation line can be hooked to a small, say 330 gallon, irrigation tank prefilled from the main tank with the exact amount of water plants in a section need. No timer is need to shut off the water, no pressure other than what gravity provides for free, no complexities to fail. KISS. Just open the prefilled tank and come back after it is emptied. When another zone needs water, quickly fill irrigation measuring tank from main tank, open valve, and irrigate the zone. The only energy input needed involves opening and closing valves.

If you live an area of adequate rainfall, then the only plants you may need to water are house plants, as it seldom rains in most homes. If not living in a dry area, catch water using 10 feet of gutter draining into a pipe connected to a 55 gallon barrel, and water your house plants as needed. Also, stop reading unless you antisipate needing to harvest rainwater for other household use.

The basics have been covered. The inventive, or merely handy, can take it from here. For details that may be worth considering, however, read on. The critical bit in a rainwater catchment system is not the guttering and PVC pipe. Most anyone on the floor at ACE or Home Depot can tell you what you need to know. The critical bit, because big and expensive in most system designs, is the "tank" thing. Most rainwater catchment tanks are too small, the biggest are 2,500 - 2,800 gallons, and may be too expensive for those who actually need to harvest rain, figure a dollar a gallon delivered and up. DIYers may turn to Craig's List and look for used IBC's (Intermediate Bulk Containers) that hold 275 or 330 gallons and go for about $0.50 a gallon. Used galvanized culvert pipe can sometimes be had, cut to about 8 foot lengths, and one end set in concrete. The inside gets a waterproof sealant, and a cover is made. Cost per gallon will be cheaper than commercial rainwater tanks, but only determined DIYers need consider this option. For cheap, look for a used above ground swimming pool, for as little as $0.03 per gallon. Put mosquito fish or other adapted fish in it and grow duckweed. Grow duckweed in floating trays and raise tilapia. A used swimming pool won't last 25 years and holes will need to be patched, but if the cost of tankage is a deal breaker, then go cheap.

For a relatively cheap and durable tank made from all new materials, SolTech Designs offers a design (free) for an above ground tank that can also be a pond. It is DIY made to whatever size is needed, for about $0.25 per gallon. Affordable tankage is key to making rainwater catchment practical, to allowing ordinary people to go green.


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