Researchers at Imperial College London said they found levels of trihalomethanes (THMs), a by-product of chlorine, in London swimming pools that were higher than amounts found in tap water that had been associated with health problems.
There have been some previous studies carried out with tap water where they found some effects like spontaneous abortion, stillbirths and congenital malformations at lower levels of these byproducts.
The by-product levels are relatively high but scientists do not know what effects THMs in swimming pools might have on pregnant women and unborn babies.
THMs are formed when chlorine, which is added to swimming pools to keep them clean, reacts with organic matter such as skin or hair.
More information is needed about THMs, which can be swallowed or inhaled, and their impact on pregnant women. In the meantime efforts should be made to reduce the levels.
Chlorine has been considered necessary to disinfectant swimming pools but the scientists said levels of THMs can be reduced by making sure people clean themselves before swimming. Filtering the water can also help to keep organic matter at low levels.
The scientists examined 44 water samples from eight indoor pools in London and compared the levels of THMs found in the pools and in tap water. Although the amount of THMs varied according to the water temperature and the number of people in the pool, it was higher than levels found in tap water.
BBC News April 4, 2002
Swimming is a wonderful sport. Many people enjoy exercising in the water.
The best place to swim is where many of our Paleolithic ancestors swam, in the ocean. The salt water actually serves to kill many of the parasites that live on our skin and in our nasal passages and eyes and takes a huge stress off our immune system. Additionally, we tend to absorb many of the valuable minerals from the water.
Unfortunately, a chlorinated swimming pool is a far inferior alternative. The chlorine in most pools is rapidly absorbed through your skin and can contribute to some major disruptions in your biochemistry.
If you don't drink unfiltered tap water, you will certainly want to avoid swimming in pools as you can absorb more chlorine after one hour in a pool than you will from a week of drinking tap water.
There are many alternatives. The simplest one would be Baquacil (most pool stores have this in stock), which is a form of hydrogen peroxide.
One could also use ozone. Both of these approaches are oxidative therapies that will kill the organisms in the pool similar to chlorine (which also is an oxidative agent).