Roofs Can Boost Rainwater Lead Levels

Tuesday, 3 March 2009

Anna Salleh ABC

On the up side, the study found 80% of tanks are probably fine when it comes to chemical contamination

Up to one fifth of rainwater tanks could have lead levels above drinking water guidelines, an Australian researcher has found.

But, he says, unless you live in a town that has a lot of heavy industry, the main sources of this lead are likely to be your roof top, rather than the atmosphere.

Robert Huston, of Griffith University, carried out the research for his PhD, as part of a project originally developed by the CRC for Water Quality and Treatment.

"I don't want people to be alarmed because most of the time the water quality is good but I think it's something that people should be made aware of," says Huston, who reports findings from the study in the journal Water Research.

Huston says previous studies have shown that lead levels in city rainwater tanks across Australia can exceed drinking water guidelines, but this is the largest study of its kind to investigate the reason for this.

He analysed 26 rainwater tanks across the city of Brisbane for chemical contaminants, with a focus on heavy metals including lead, cadmium, zinc, iron and copper.

"About 10-20% of tanks at any one time have lead above the Australian Drinking Water Guidelines," he says.

Atmospheric fallout

Huston also analysed the atmospheric fallout occurring at the same time and place as he was collecting rainwater tank samples and found this did not account for the high lead levels.

He then added up all the sources of lead in the environment and modelled how it was dispersed, analysed lead isotopes and performed statistical analyses to help work out where the lead was coming from.

Putting all this together he concluded that most of the lead was coming from rooftop sources such as lead flashing and leaded roofing nails.

"Industry and cars are certainly a source but they're not the main source as far as lead goes in places like Brisbane," says Huston.

He says that rainwater in towns that have heavy lead pollution from industry would obviously have a higher level of lead coming from the atmosphere.

The study also found levels of zinc also exceeded drinking water guidelines.

Improving tank water

Huston says the quality of treated water is more reliable that tank rainwater but says there are things homeowners can do to improve the quality of their tank water.

• Remove any lead on the roof or cover it with lead-free roofing paint.

• Use a floating outlet from the tank that takes water from near the surface (he says this will protect from Cryptosporidium cysts as well as from lead, both of which tend to fall to the bottom of the tank).

• Use an ion exchange filter, but this must be changed regularly.

• Use a concrete tank which keeps the pH of the water alkaline and precipitates lead, which is a problem when water sits in plumbing with lead solder. He says plastic tanks tend to have lower pH, which makes lead more soluble.

• Flush pipes before drinking.

Huston says apart from chemical contamination, the other concern about rainwater has been microbial contamination from animal faeces.

But he says, a large epidemiological study in South Australia found no evidence of increased gastroenteritis among rural children who rely on rainwater, as compared with urban children who drink treated water.

Source: ABC Science News