Water Tanks Require Cleaning
The primary focus of maintenance procedures should be to keep all components clean and to minimise the risk of contamination/rubbish either entering or remaining in rainwater tanks
As per Section 6 the catchment area should be kept clear of debris. The roof should be washed clean once or twice a year and in particular should be cleaned toward the end of the dry season. Gutters should be cleaned regularly to remove leaves, collected dirt etc.
In areas subject to large amounts of wind-borne dust the roof and gutters may need to be cleaned more frequently.
Inlet screens and first flush/bypass devices should be cleaned regularly and kept in good repair.
All tanks should be examined for the accumulation of sludge every 2-3 years, or if sediment is evident in the water flow. Sludge can provide an environment for survival and/or growth of micro-organisms and in some cases relatively high concentrations of lead have been detected in sludge even though the body of stored rainwater complied with drinking water guidelines.
Outlet taps are generally near the bottom of tanks and as sludge accumulates the likelihood of material being re-suspended and being removed with rainwater increases. Concentrations of lead exceeding the Australian Drinking Water Guidelines (NHMRC/ARMCANZ, 1996)
have been detected in water containing barely visible particulates of sludge that were resuspended by water flowing through the outlet tap.
Sludge may be removed by siphoning without emptying the tank. To do this, use an inverted funnel in the end of a hose and move it carefully across the bottom of the tank. The sludge plus the lower portion of water in the tank can then be released to waste. If leaves and coarser debris are present in the sludge, a siphon hose of approximately 50 mm diameter should be used.
Sludge may also be pumped from the tank with minimum loss of water by using a suitable motor operated pump and attachments.
Finally sludge can also be removed by draining and cleaning the tank. If a drain plug is provided at the base of the tank, water can be run to waste to discharge the sludge. Once the tank is empty, the remaining sludge can be scooped up and removed through the access opening. Care should be taken not to disturb the protective film on the inside surface of steel
tanks.
Professional tank cleaners (generally listed in telephone directories) may also be available to de-sludge tanks.
Organic material removed from the tank may be disposed of in the garden by spreading and digging into garden beds. Alternatively sludge should be disposed of at a licensed waste depot.
Where cleaning necessitates entering the tank, care should be taken to ensure adequate ventilation is provided and an additional person is in attendance. Advice on working in confined spaces should be available from Occupational, Health, Safety and Welfare authorities in each State and Territory.
It is important to check the structural condition of the tank before choosing a method of cleaning. Harsh cleaning methods may accelerate deterioration. In the case of a steel tank, removal of the protective layer on the inside walls will lead to tank corrosion.
Cleaning agents that might release hazardous fumes or adversely affect water quality after cleaning should not be used. After cleaning it is recommended that the internal walls and floor of the tank be rinsed with clean water. Rinse water and sediment should be run to waste.
Discarded water should be diverted away from tank foundations, buildings and other structures.
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