Introduction
A tank is a type of storage used in domestic, commercial and/or industrial settings to store water collected from surface runoff or sources such as greywater or blackwater waste streams. Once stored the water can be released in a controlled manner, and/or used to supply water demands.
There is a trend towards installing domestic rainwater tanks in urban areas to capture roof runoff and supply non-potable water demands. The benefits of using water sourced from a rainwater tank include:
- reduced reliance on potable water supply, thus deferring potable water system upgrade or expansion and increasing the security of supply from existing water sources;
- stormwater retention/detention;
- urban water quality improvement via retention and diversion of stormwater to the sewer and garden areas, thus reducing the volume of stormwater pollutants discharging to the catchment watercourses; and
- protection of urban streams, through reducing the duration of elevated flows.
Rainwater tanks are most efficient when the retained water supplies multiple water demands within a household, eg toilet flushing, garden irrigation, filling or topping-up swimming pools, clothes washing and other appropriate non-potable uses.
In many areas health departments do not expressly prohibit rainwater tanks supplying drinking water, however, guidelines typically recommend avoiding drinking rainwater where a reticulated potable supply is available.
Tank construction
Rainwater tanks are usually constructed from plastic, or galvanised steel, and are located above-ground adjacent to the sides of a dwelling or building. Where space is limited, tanks can also be installed below-ground, under-floor and in-slab - in these situations, tanks are often constructed from concrete or impermeable plastic membranes.
Conceptualisation
Conceptually, the operation of a rainwater tank is identical to the operation of any tank-based storage infrastructure. The simulation scheme developed is generic in its applicability to all forms of tank-based storage. The tank allows for the inflow of rainwater as well as the provision of trickle top-up, triggered to start and stop at a user-specified tank level.
Tank Technical Details
First Flush Separation
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Vff is the diameter of the first flush outlet (m³);
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The Urban Developer storage tank, shown in Figure 2, breaks the available storage volume into three distinct storage zones.
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fdetention outflow is diameter of the outflow orifice (m).
Acknowledgements
This material has been adapted from:
eWater Cooperative Research Centre (2011) Urban Developer Product Specification: Storage Tank Routing v0.4. eWater Cooperative Research Centre, Canberra. 23 June 2011.