They are picked up as rainwater makes its way through the soil and as it flows in streams and rivers. Most bacteria are harmless but some are not. If water carries disease causing organisms it can seriously damage our health. So we treat water in treatment plants to remove harmful bacteria from drinking water. One of the most effective ways of making drinking water safe is to add carefully controlled levels of chlorine.
Chlorine is a very safe and efficient way of killing bacteria in water supplies.
It has been used in the UK since 1897. It is safe because in controlled doses it is deadly to bacteria but harmless to us. It is efficient because once it has done its job, it gradually disappears from the water. We have taste panels at our laboratories. Some people can taste chlorine in drinking water more readily than others.