The presence of suspended material or the generation of off-tastes and odours from accumulated material or algal growth can affect aesthetic quality. The possible presence of suspended material can be minimised by keeping the roof catchment reasonably clear of accumulated debris, including leaves and twigs, and by keeping gutters clean. Roofs and gutters should be cleaned twice a year or more frequently in areas subject to large amounts of windborne dust or leaves.
Generation of tastes and odours can be prevented by:
- keeping gutters clean and ensuring they drain quickly between rain events
- preventing entry of light into tanks or pipe work; some types of white pipes allow transmission of light and should be painted a dark colour
- removing accumulated sediment
- installing pipe work so it is self-draining or installing drainage points to enable pipes to be emptied and flushed.
Removing odours and suspended materialIf rainwater has a distinctive odour or contains suspended material, the most likely sources are accumulated material in gutters, or at the bottom of tanks, or stagnant water in pipe work that does not self-drain.
Corrective action should include inspecting gutters and the bottom of tanks and determining whether there is pipe work that can contain stagnant water. If necessary, gutters and tanks should be cleaned and pipe work drained. Where possible, a drainage point should be fitted in pipe work that does not self-drain.
It is not always practical to clean a tank immediately, particularly if it is the only source of drinking water. In addition, off-odours from pipe work and accumulated tank sediments are more common in hot or warm weather in the absence of likely replenishing intakes of water. In this case, chlorinating the tank can provide a temporary solution until cleaning can be undertaken (for example, at the beginning of winter or the wet season). Any pipe work, including inlets to tanks, that does not completely drain, should be flushed with chlorinated water. The dose rates in Section 5 are suitable.
Many of the taste and odour issues associated with tank water are caused when dissolved oxygen levels in the water become low, and anaerobic processes begin to dominate. In some cases the taste and odour issues can be resolved by pumping air into the water to increase the amount of dissolved oxygen in the water. This will require access to a pump and the ability to insert an air hose into the tank. Care should be taken to avoid adding the air at such a rate, or at such a depth, that it disturbs or stirs up sediment on the bottom of the tank.
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Bushfire debrisAsh and debris deposited on a roof should be removed and the first flush of water after a bushfire should not be collected. If material has been washed into a tank in sufficient quantities to affect taste or appearance of rainwater, the tank will need to be drained and cleaned, or alternatively the water could be used for non-potable purposes.
Where rainwater tanks are used in the bushfire-prone areas, consideration should be given to ensuring that the rainwater can be easily and quickly disconnected from the roof area for the tank. The disconnection should occur as early as possible when a bushfire is in the area so as to avoid windblown ash or debris landing on the roof area and possibly entering the tank.
Reconnection of the tank to the catchment area should only occur after the fire has past and the roof area has been clear of ash and debris.
Fire retardants and foams may also be deposited on roofs. This material can be washed into tanks when water is hosed on to the roof as part of fire protecting activities, or when it rains after a bushfire.
The recommended concentrations of the commonly used retardants and foams should not present a risk to health, but they may affect the taste of the water if washed into the tank. Fire retardants also contain detergents that may cause the water in the tank to froth.
Rainwater in tanks that have not been affected by ash and debris, and has no taint or odour can still be used for normal purposes.