Rainwater Harvesting FAQ's
A RWH system consists of four elements, a collection area, a conveyance system, storage facilities and a distribution system.
As most RWH systems are designed to capture rainwater from the roof of buildings, materials used can affect the quality of the water produced. Slate or concrete tiles can affect the acidity of the water produced and can make a difference in water treatment requirements. In the case of retro fitting on existing buildings zinc and lead flashings need to be covered with a sealant to prevent leaching into the water.
The amount of roof space dedicated to the RWH system will determine the amount of water produced. The starting point to remember is that a family of four persons uses 1000 galls of water per week, the majority (approx. 80%) used for toilets, washing machines and dishwashers.
In the case of retro fitting it would perhaps be sensible to introduce the rainwater only for flushing toilets, piping the water directly to the toilet cisterns. This would substantially reduce the existing water consumption with little disruption to the existing pipework. A water analysis to check the acidity of the water is essential.
To take full advantage of the facility, based on the average usage (1000 galls per week) a minimum storage tank of 8000 litres is recommended. (Tanks are available in much larger sizes as required). This would provide two weeks water supply.
Dedicating the area of roof space will determine the amount of water collected. An example: 2 roof areas of 15mtrs (50 feet) by 9mtrs (30 feet) in Cavan County where the mean annual rainfall is 1030mm would produce on average 610 litres of water per day. (Monthly/annual water data can be obtained: http://www.met.ie
270 cu mtrs x 1.03 x 0.8 (efficiency) divided by 365 = 0.61 cu mtrs (610 ltr)
The usual guttering, down pipes and ground works provide the conveyancing
element, transferring the water to the storage tank which can be inside, outside, above or below ground.
It is important that the rainwater be as clean as possible so that it is safe for later use. The answer to ensure cleanliness is to install a 'first flush' device between the guttering and the storage vessel. This can be as simple as a small tank 20/30 gallons that intercepts the water supply allowing the 'first flush' to be excluded from the main water collection.
The illustration shows how the
device works. A small tank placed on a block plinth would enable the 'waste' water to be
used for the garden.
A number of uses have been recommended for collected water: flush the toilet, wash ther car, wash clothes, water the garden. Personally, I would not wash my car in water that may by acidic or wash clothes especially those of children in untreated water.
Before deciding on the extent of using collected rainwater the removal of any bacterial or contaminant risk to the user is essential. If you choose just to flush toilets there is still an inherent risk in having an untreated source inside the building whether in domestic or commercial applications.
We have been involved in a number of trials that have been successful in producing high quality water from RWH and can supply various size units for both domestic and commercial applications and to accommodate the choice of usage of the collected water, whether it be for grey water use, toilets, etc. or general applications.
The complete system including storage tank, c/w pump, controller, prefilter, vermin trap and calmed inlet €3950.00 + VAT. Additional filtration
equipment will be extra and depend on the water quality desired.