Lead in drinking water is mostly caused by lead pipes especially in houses built prior to the 1930s. The lead concentration is normally higher when the water is softer, ie. has a lower pH. When lead enters the body it can cause damage to the central nervous system as well as cause developmental harm especially in children and infants, neurological and kidney damage. Once lead has entered the body it is released very slowly, which means ongoing exposure will cause a build up of lead in the body.
The amount of lead in water caused by lead piping is greater when the water has been sitting in the pipe for a while, ie. in the first water of the morning. It is therefore important to let the water run to flush the pipe before using it. Because lead levels in the water can vary throughout the day, it is recommended to test your drinking water more than once - ideally throughout one day whenever you use your water for consumption.
The UK maximum contaminant level for Lead in tap water set by DWI/DEFRA is 10µg/l (= 0.01mg/l = 0.01ppm).
