When you want to install a water tank it is important to establish whether there are any local health, building or planning regulations associated with rainwater tanks. The local council or regional authority with jurisdiction over these regulations should be consulted.
In some rural areas there may be requirements associated with supply of water for firefighting.
Connection to the Town Water Supply
Water authorities usually do not allow direct connection of rainwater systems with reticulated water supplies or alternatively require the use of backflow prevention devices to stop rainwater siphoning back into the reticulated supply. If in doubt information should be sought from the local water authority.
Contamination Risks
Rainwater tanks should be installed in a manner that will minimise the risk of contamination from industrial pollutants, dust, leaves, pollens, pesticide sprays, fertilisers, debris, vermin, birds, small animals and insects. Tanks should not be allowed to provide breeding sites for mosquitoes.
Underground Tank Location
Underground tanks require additional protection against entry of surface run-off or groundwater, animal or human faecal material and soils. These tanks need to be properly sealed and access points need to be protected against ingress of surface run-off. Maintenance and cleaning of underground tanks may be more difficult.
Access Points
Tanks should have impervious covers and all access points except for the inlet and overflow should be provided with close fitting lids which should be kept shut unless in use. The inlet to the tank should incorporate a mesh covering and/or strainer to prevent the access of mosquitoes and other insects and to prevent material such as leaves etc that may have
collected on the roof or in gutters from being washed into the tank. The overflow should also be covered with an insect-proof mesh.
Sunlight
Tanks should be light proof to minimise algal growth. Most algae will not make water unsafe for human consumption but can adversely affect the taste, odour and appearance of the water.
First Flow/Flush Divertors
After any extended dry period it is good practice to let the first run-off of rain bypass the tank. This first rain will wash the roof catchment and may contain higher than average amounts of accumulated dust, bird and animal droppings, leaves and other debris. It has been shown for small roofs that the water quality improves once the first 5 litres of water has passed through the down-pipe from the roof guttering (Yaziz et al, 1989). For an average roof catchment it is suggested that the first 20-25 litres should be diverted/discarded.
First flush diversion devices are commercially available and the installation of such a device should be considered as a means of improving water quality collected in tanks.
Water Tank Overflow
The inlet pipe to all rainwater tanks should be easily detachable so that when required the tank can be bypassed.
Run-off that is not collected in the tank or that overflows should be diverted away from tank foundations, buildings or other structures. This water should be directed onto gardens or into the stormwater drain; it should not be allowed to pool or to cause nuisance to neighbouring properties or to areas of public access. Local authorities may have regulations or requirements that apply to diverted or excess rainwater flows.
Inlet Pipes
Wherever possible all sections of inlet pipes should be directed down and rainwater should flow into the top of the tank. The inclusion of rising sections will provide potential traps for sediments, biofilms and stagnant water and these should be avoided. Modifications to existing downpipes should not restrict existing water flows from roof gutters. To maximise
the collection of rainwater the downpipes should be of sufficient diameter to accept all of the water flow from roof gutters, even in heavy rains.
Roof Catchment Areas and Gutters
Roof catchment areas should be kept clear of overhanging vegetation to reduce the amount of leaves and debris falling onto the catchment area. Overhanging branches also provide access to the roof for rodents, cats and possums and can provide roosting points for birds.
Gutters can be shielded from large debris (bark, larger leaves, etc) with plastic mesh but smaller particles will still accumulate and require regular removal.
Gutters should have sufficient and continuous fall to downpipes to prevent pooling of water which could increase accumulation of material, lead to algal growth and possibly provide a site for mosquito breeding. A fall of one in a hundred to one in five hundred should be sufficient.
Overflow, discharge or bleed-off pipes from roof-mounted appliances such as evaporative air conditioners, hot water services, and solar heaters should not discharge onto the rainwater catchment area.
Multiple Rain Water Tanks
Tanks of different sizes and shapes can be interconnected to enable the use of one water pressure pump, resulting in a big cost saving. Additional tanks can be installed and connected at any time to an existing system.
Modular tanks are specifically made to add new tanks as your demand increases.
Compulsory Water Tank Installation
State Governments and Local Authorities are implementing legislation that will require every new home to have a water tank installed. If youre building a new home, check with your builder about local legislation.
Water Tank Stands
When considering a stand for your water tank you need to take into consideration the size of the size of the tank and how much it will weigh when full, as the tank stand has to be able to support the weight.
1 litre of water weighs 1 kilogram which means that a small 3000 litre tank will weigh 3 tonne and even a medium size 10,000 litre tank will weigh 10 tonnes when full.
With this sort of weight involved it is important to correctly install or construct your tank stand.
Different types of tank stands include:
- Concrete Slab
- Corrugated steel ring filled with crusher dust
- Crusher dust base with support edging
- Precast concrete slabs
- Timber and steel tank stand. Please note, that because of the weights involved these generally require an engineer design and building approval.
Three points of caution:
- Generally sand should not be used as a tank support.
- Before proceeding with an elevated stand, check with your local authority as regulations differ between areas.
- Consider how much weight the stand will have to support.
Where to Install a Water Tank
A water tank can be a rather large and bulky item depending on the quantity of water required, and the location of the tank affects the tanks ability to collect water. Depending on the size and shape of the selected water tank, it is best to locate it as close as possible to an existing downpipe.
A tank up to 5000 litres generally requires only one down pipe provided it drains a suitable roof area. Larger tanks perform better with multiple downpipes attached. If attaching multiple downpipes, check if access is available to the tank. Do you have an existing concrete or paved level area on which to install your water tank?
Access for the delivery of the tank also influences the type of tank installed. If your tank will be behind buildings, consider the access space between buildings and fences. If access is difficult, the tank can be delivered via a neighbouring property, and sometimes a crane will be required.
Your choice may be determined by access. Due to the many varying sizes of water tanks it is easy to find a tank size that will fit just about anywhere. Make sure your supplier has a range of options rather than offering a One tank fits all solution.
The life of a tank is dependant upon many factors and a little care in the choice of the location of the tank can often mean a difference of many years. Whenever possible tanks should be installed in a cool position, preferably on the southern side of a building, away from trees from which leaves might clog the strainer or contaminate the water.
Direct sunlight falling on a tank for long periods on a hot day can create temperature differentials in the water. This can affect the performance of the tanks. All overflow water must be piped away from the tank base regardless of the tank type.
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