Potable Water System 1 – Recommendation
The residence has approximately 114 sq m (1,225 sq ft) of catchment from metal roofing. Two 11,300 litre (2,500 Imp gal) cistern tanks hold the harvested water, which passes through a settling chamber just after a first-flush chamber. A pump, pressure tank, filters and UV light are installed and working, and water quality tested from one lavatory tap show excellent water quality. An analysis of the system, however, points out several aspects that are not up to ‘standard’, even though at installation this may have been state-of-the-art.
The existing rainwater harvesting system overall cannot completely support two people under fairly normal usage, which in this case excludes outdoor uses and hot tub, plus an estimate for overnight guests. A total of 130,000 litres of potential annual catchment is possible, calculated using an 80% efficiency factor. A total of 111,000 litres is estimated as the demand, for flushing, bathing, cooking, and clothes washing. However, seasonality of the rainfall and limitation in storage mean inadequate supply to meet demand.
Additional catchment area and storage capacity are required to meet projected demand on the system, along with a number of other items. Tanks should be inspected for sediment, based on the lack of good pre-filtration, and gutters should be checked and cleaned of tree debris.
Recommendations include revamping conveyance piping that has sags and is supported only by industrial strapping; the addition of downspout (or conveyance) filters; replacing the settling-tank filter with an upright first-flush vortex filter; replacing the inter-tank connection piping to match inlet piping size; adding overflow connections for the tanks and filtration; installing an additional tank to harvest more of the overflow from the existing roof catchment; and accessing additional catchment area by using the rainwater system shed metal roof area.
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