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It is, however, important to note that the level of lead exposure resulting from a contaminated rainwater tank is relatively low.
“Lead exposure from drinking rainwater is relatively low and unlikely to cause serious damage over short periods,” Robert says.
“The most sensitive subpopulation of lead toxicity is children. Low level exposure to lead affects cognitive development leading to lowered IQ, poor concentration and behavioural problems at school – although they may be relatively subtle effects depending on the blood lead levels. Poor nutrition can exacerbate these toxic effects.”
As rainwater tanks become ever more popular it pays for plumbers to keep abreast of new research findings that place them in the best position to offer sound advice to their customers.
The most obvious solution to the problem is to remove lead flashing from roofs where possible.
“If you can’t remove the lead flashing the next best thing is to seal it over with a lead free paint or polymer membrane. Stop the contact with rainfall and the atmosphere and you will stop the main source contaminating the tank,” Robert says.
“If you have high lead paint it’s a little trickier. Painting over it is a partial solution but over time it will degrade and expose the lead paint, so removing it or stripping it back is really the best option.”
Most of the lead entering a rainwater tank settles to the bottom with the sludge, for which Robert has an innovative solution.
“If you can raise the outlet 500mm from the base you tend to avoid most of the sludge. A ‘floating’ outlet that consists of a flexible tube sitting inside the tank so that the draw off point is about 10-20cm below the surface of the water, which obviously rises and falls depending on the level of the tank, is an even better option.
Additionally, adding lime to the tank to modify its ph level may help, but this has not yet been tested in the field, he says.
“The evidence comes from concrete water tanks. If you can get the ph level above seven the lead will precipitate out and end up in the sludge. As long as you have a draw off point that is avoiding the sludge entering the water at the outlet it should solve the problem.”