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potable rainwater harvesting system for client with 'homemade' tank, first flush, uv sterilizer  RSS feed

 
Corey Schmidt
Posts: 155
Location: Kachemak Bay, Alaska (usda zone 6, ahs heat zone 1, lat 59 N, coastal, koppen Dfc)
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This is to document a potable rainwater catchment system I implemented for a client's cottage in kachemak bay, AK. We have had warmer winters and drier summers lately and the community wells have not been as reliable as in past so there is a growing demand for rainwater catchment systems.
Water is collected from roof thru a purchased screen and first flush diverter. primary collection tank is about 350 gallons. it is built of 2'x4' welded wire fencing, bituthene, 6 mil polyethylene sheeting, black polyethylene water tube to create and maintain circular shape, and plywood lid with roof made of salvaged onsite materials. A submersible pump (make sure to get Oil free if you go this route, just in case the pump eventually breaks) sends the water thru 20,5,1 micron nominal filters to larger holding tank. The pump is on a gfci protected circuit and there are float switches in both tanks such that for the pump to come on, the big tank (previously installed by client) needs to be NOT full and the new catchment tank needs to be about 1/3 full (adjustable depending on float switch installation). Catchment collection tank is slightly higher than main storage tank, but not high enough to get adequate pressure through filters. Still there is potential for siphoning to continue after pump turns off so a reverse check valve was installed so that once siphon action begins, air is sucked in the line breaking the siphon. Clients have a pre existing prefilter after the water leaves the main storage tank, and a 1 micron absolute 8 gpm filter was installed after the house pressure demand pump followed by an 8-10gpm rated uv sterilizer. Over flow from catchment tank goes to a garden area and first flush device drains to a french drain leading to a microswale away from the house foundation. more fotos to follow.
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home made catchment tank
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catchment tank detail, inlet, outlet, reverse check valve
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screen, first flush, french drain, main cottage tank in background
 
Corey Schmidt
Posts: 155
Location: Kachemak Bay, Alaska (usda zone 6, ahs heat zone 1, lat 59 N, coastal, koppen Dfc)
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more fotos.

float switch in the clear tank deactivates the outlet when the tank is full and activates circuit when the level drops about 9 inches below overflow. Float switch in the catchment tank activates circuit when tank is about 1/3 full and deactivates circuit when about 1/8 full. For pump to work, catchment tank needs to have water in it and main tank needs to have space in it. this combined with overflow pipe to garden makes the system fully automated other than purging the first flush device and spring startup and winter shutdown. Catchment tank is built of flexible inexpensive materials so it can freeze without problems, but its performance when full in deep freeze conditions (fairly rare here) is still untested. a conservative management plan might be to open first flush purge valve after clients leave in the fall and the catchment tank is 2/3 full so it does not freeze when totally full (which means about 4-6 inches from water level to lid.)
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filters
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pump, big blue filter housing with absolute 1 micron cartridge, UV sterilizer
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gfci protected float switch controlled receptacle
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