As we become more aware of our ecological footprint, many new builds and redevelopment projects now include rainwater harvesting facilities, to reduce household water consumption. Planning or project managing such an installation requires a good understanding of the key components of a rainwater harvesting system. Choosing the right system for each individual location will ensure a high quality installation and long term customer satisfaction.
How Rainwater Harvesting Systems Work
The roof of the building provides the surface area for rainwater collection; from which the guttering directs the flow to the downpipes, for filtration and collection in a tank. The collected water is pumped back into the property for external use, or to supply washing appliances and for toilet flushing.
Average rainfall, water consumption and roof surface area are used to calculate the required tank capacity. Each system component is then tailored to meet the needs of your client.
Above Ground or Below Ground Tanks
Harvested rainwater can be stored either above or below ground. Factors which determine the correct type of tank include whether the plot is large enough to bury a tank, and the site’s suitability for excavation.
Below ground tanks come in a range of sizes, depths and capacities to suit the requirements of any domestic or commercial property. They can be plastic, fibreglass or even concrete.
Above ground tanks include standard uninsulated plastic storage tanks, insulated one piece tanks or sectional insulated tanks. Sectional tanks are more expensive but very versatile as they can be fitted together to suit any space.
Filters prevent leaves, insects and other debris and from contaminating the stored water, which could otherwise lead to the growth of anaerobic bacteria. Filters can be downpipe filters, pre-tank (e.g. Vortex) filters or in-tank filters, and must be capable of filtering out particles greater than 1mm or even smaller. Some are able to filter down to 0.28mm. If even finer filtration is required this must be done post-tank using the pressure from the pump.
If the building has sufficient space at high level to accommodate a header tank, a gravity fed system can have advantages in some situations. With this type of system the backup from the mains cold water supply will go to the header tank, not to the main storage tank.
It is important to understand that with this arrangement the pressure available will depend on the height of the header tank above the outlet i.e. 10m = 1 bar (14.5 psi)
A break tank is similar in as much as it provides the interface with the mains water backup supply. The break tank is used in conjunction with a booster pump set so that the water can be delivered at the pressure and flow rate required, and are sometimes combined into a single unit, though this offers limited flexibility. Break tanks can be situated at any level but are generally located within a ground floor plant room.
Pumps & Pump Controllers
Pumps transfer the water from the storage tank to either a header or break tank, or to each water point in a direct fed system. Submersible pumps are quiet and efficient and are preferred for getting the water from the main tank as this allow the tank to be a greater distance away from the building.
Pump controllers activate the pump by detecting the fluctuations in pressure when an outlet is opened or closed. Commercial properties may require a controller capable of operating multiple pumps and other components of the system.
Float Switches & Float Valves
Float switches and valves regulate the flow of rainwater and mains water into a header or break tank, to provide a constant supply of water during periods of lower rainfall, or during a drought. Float switches are used to activate a pump or solenoid valve, or to provide dry-running protection. Float valves can also regulate the flow of water but being mechanical require no electrical connection.
Backwater Prevention Valve
To comply with the British Standard underground rainwater storage tanks must have a back-flow prevention valve in order to stop contamination by ground water entering the rainwater storage tank. An anti-back-flow device uses the downstream water pressure to close the valve.
You’ll need to calculate the amount of piping required to connect the building with the tank, and to install internal piping for each utility area. Ensure that water regulations are complied with by using identification tape and labels on pipes and outlets.
Additional Specialist Equipment
There may be a need for other equipment in some installations, e.g. for monitoring or disinfecting. In some situations where an aerosol spray may be created or where wholesome potable water is required, UV sterilisation or similar is recommended.
Rainharvesting Systems can provide advice and expertise on every system component. Once you’ve considered the key determining factors; location, space and usage, we can provide everything you’ll need to create the perfect solution for every individual project. For more information, please refer to our Guide to Rainwater Harvesting Systems, which can be downloaded by clicking here.