Rain Collection System

I’m sure several of you remember Mark from his compost barrel tutorial posted here.  I invited him back to talk about his rain collection system. Bonus – its nerded up with math!

For the gardener, summer droughts can really be disheartening.  One is left with the choice of watching plants wilt or using whatever water is quickly available (i.e. tap water or using water from your home’s well).  Another, and arguably best, solution is to harvest natural rain water.  There are several key advantages of using rain water, especially on food crops.  If you are on a municipal water system, your supply has had chlorine and probably fluoride added.  If your home is on a well, a high mineral content is possible.  Also, when the annual “dry spell” comes many cities turn to water restrictions—resulting in fines if someone is caught watering lawns, gardens, or washing vehicles.  Of equal importance, a drought, by nature, puts a strain on a home’s well.  This is only compounded if large quantities of well water are used to sustain a size-able garden.
My rain barrel systems consists of three 55 gallon barrels all connected together at the bottom so the water level stays the same in all, regardless from which I chose to draw water.  I decided it was best to pour a concrete slab for them as well.  Water is heavy.  Each gallon weighs 8.34 lbs.  When full, the system contains roughly 160 gallons, which is a total weight of over 1,300 pounds!  A slab ensures they won’t begin to lean, tilt, or begin to sink into the ground as time goes by.  The rightmost barrel (the black one) is filled from the gutter’s downspout via a diverter made by Rainreserve, found here.  I chose this particular diverter because it fit neatly inline with the downspout and, when installed level with the barrel’s inlet, the excess water flows on down the same gutter when all three barrels are full, thus, eliminating the need for separate overflow piping.  I keep lids on all the barrels to prevent evaporation and help keep bugs, leaves, etc. out of the water supply.  Since the lids seal tightly, I drilled three small vent holes in the front of each barrel about two inches down from the top.  Without the vents, air pressure would build inside and interfere with filling during a hard rain.
So, how much water does the prudent gardener need to try collect?  No set-in-stone answer exists, but a bit of math will help guide us.  The total area of my raised beds is 72 square feet.  If I want to give them the equivalent of ½ “ of rain, I multiply 72 times 144 (this converts square feet into square inches) and I get 10,368 sq.in.  This multiplies by the amount of rain I want to duplicate, in this example ½”.  The result is 5,184—this number is cubic inches of water.  We then divide 5,184 by 231 (one gallon = 231 cubic inches) and we arrive at 22.4 gallons.  This tells me that in order to emulate ½” of rain on the 72 sq.ft. of my raised beds, I will need to use 22.4 gallons.  Since my system holds about 160 gallons, I can use 22.4 gallons just over seven times until the barrels are empty.  What does all that mean?  Assuming I water every other day, I can sustain my gardens with the equivalent of ½” of rain, at each watering, for a full 14 days without a drop of water falling from the sky.
The styles and processes of collecting rain water are plentiful.  Some systems are elevated to create a gravity fed scenario which allows a garden hose to be attached and the water naturally flows to its destination.  I set mine up to intentionally give me the exercise of carrying water to the gardens.
 One last note; rain water is “soft”.  That is to say it doesn’t contain calcium, magnesium and other minerals.  If you have ever looked into making your own lye soap, you’ll know it requires soft water—your rain water is the perfect source.


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