Summer's coming, the mercury's rising, and every time your children cool down in a swimming pool, they risk their lives.

Ditto, every time they drink tap water, which they'll do more in the hot days ahead.

That, at least, is what anti-chlorine lobbyists would have you believe. They say the chlorine in the water you and your family use to drink, shower, bathe and swim in, accumulates in your bodies, and chips away at your health till your defences crumble.

Scientists have another perspective. They say levels of chlorine in your potable (drinking) water comply with international safety regulations. They also point to the substantial dangers of not chlorinating drinking water, and say that while chlorine levels may be higher in swimming pools, you'd have to drink an awful lot of pool water to be at risk.

Karl Lubout says it's all about "balance of risk". He is manager of water quality marketing for Rand Water, that produces Gauteng's drinking water - over 3 400 megalitres of it every day - and the same water that goes into our pools.

He says water-borne disease, such as cholera or typhoid, is still the number one killer across the globe, far greater than Aids. Chlorine effectively kills the bacteria that cause water-borne disease.

He also says that the amount of chlorine present in your drinking water (a concentration at the tap of 0,3 to 0,6mgs per litre) is proven to be safe.

Yet concerns about our water continue to ebb and

flow. They rose recently after rainfalls in Gauteng left a layer of noxious-looking white stuff on cars, roofs, lawns and swimming pools; they subsided when officials said there were no reports of it near to catchment areas to pose a threat.

(Scientists say it could have been a form of "acid rain": dissolved gases and pollution in the air that collect in the atmosphere and come down in the rainfall, but I couldn't find anyone who actually collected it and had it tested.)

So just how real is the threat of chlorine? Very, if a local website (www.chlorinefree.co.za) is to be believed. It says chlorine was used to "kill people by burning during World War 1", yet now we drink it, swim in it and wash in it.

It says that when chlorine is added to drinking and swimming water, it combines with other chemicals and natural compounds (like leaves) in the water to form carcinogenic trihalomethanes (THMs) and other by-products. These trigger the production of free radicals and cause cell damage.

And while concentrations of these carcinogens are low, it is precisely these low levels that scientists believe are responsible for "the majority of human cancers in the US", the site says. It says further that "skin absorption of contaminants in municipal water has been underestimated and that ingestion (drinking) may not constitute the sole or even primary route of exposure".

Among problems associated with chlorine are asthma-like respiratory conditions, skin problems, miscarriage, birth defects and cancer. The site also says chlorine doesn't even do a good job of purifying pool water. All it really does is "bleach the dirt in your pool, giving the appearance of clean water that belies the fact that the water you're swimming in is potentially hazardous to your health and your family's wellbeing".

That may sound somewhat alarmist, but there are many sites with references to back up concerns. Still, other scientists say chlorine should be seen in its proper perspective.

Environmental and chemical consultant Dr Dave Baldwin says there is a lot of hype about chlorine and it has "proven itself" for water treatment. However, it is not a "wonder chemical" and there are issues surrounding its use.

For starters, one of the THMs chlorine produces when it reacts, is chloroform, the very same stuff doctors used to anaesthetise patients in the old days. It is recognised as a "possible human carcinogen". This is more of a problem for swimming pool rather than drinking water, because of the presence of leaves and other organic matter with which chlorine reacts to form chloroform.

Chloroform levels depend on a variety of factors, including how well a pool is kept clean, says Baldwin. Also, chlorine levels reduce when exposed to sunlight (which is why you put chemicals in after sunset).

And while you don't usually drink swimming pool water, you do ingest it, Baldwin says.

Competitive and professional swimmers are more at risk because they spend more time in pools. They also breathe more deeply while swimming, and are thus likely to take in more of the pool waters' vapours.

Changing to so-called "salt pools" won't help much, says Baldwin, because the pools use an electrolysis unit that changes sodium chloride (common salt) used into chlorine.

There are non-chlorine alternatives on the market, he says, but you can reduce the risk by keeping your pool scrupulously clean.

Lubout says he is not saying there is "zero risk" attached to the chlorine in tap water, and some people are more sensitive to it than others. However, while it is true that chlorine is toxic in massive doses, he points out that the same applies to ordinary table salt and other natural substances.

Lubout says our drinking water is purified using a conventional purification process that includes disinfection. Rand Water uses chlorine to disinfect drinking water, as do other countries, according to strict guidelines laid out by the World Health Organisation. He also says there are "few guarantees like the one you get for water": A person weighing 75kg can drink 2 litres of water a day for a lifetime, with no ill effects.

Ayesha Sasman, national information office for the Cancer Association of South Africa, says the association has seen no strong evidence of a causal link between chlorine and cancer, and does not advise against drinking tap water or swimming in chlorinated pools.