The Water Supplies Department held a demonstration for the media today to show the comprehensive measures it takes to ensure Hong Kong's water supply is safe.
The department's Chief Chemist Chan Kin-man said tests are conducted according to World Health Organisation guidelines and under very strict conditions as contamination, such as dust or dirt, can make a big difference to the result.
It collects samples in specially-made bottles that are soaked in concentrated nitric acid for four hours and rinsed with deionized water to ensure the purity of the sample.
When collecting samples from taps, the water is left to run for five to 30 minutes before the sample is taken.
The department's officers then use a mass spectrometer to analyse the metallic elements in the water. The $2 million spectrometer can detect even the smallest amount of metal in the water.
Mr Chan said these steps are essential to ensuring the accuracy of the tests.
