A fifth of Hong Kong families often experience impurities and discolouration in their tap water, according to a survey on drinking water quality. The New Forum phone-interviewed 1,461 residents aged 15 to 65 about the quality of their household drinking water last month and early this month. Tests prompted by complaints showed that a high iron content had caused noticeable colour and turbidity in water samples collected from several Kwun Tong estates, according to the group. But the Water Supplies Department said the average iron value in water supplies across Hong Kong was very low. More than 21 per cent of respondents said they often found their drinking water to be yellowish, while 18.8 per cent said they often found impurities. About 14 per cent of respondents said they often detected a suspicious smell and taste in their drinking water. Some 8 per cent of respondents reported having all of the above. 'We can infer that about 170,000 families often experienced the situation based on the fact that there are 2.2 million families in Hong Kong,' said New Forum member Ng Yuen-tat. More than 63 per cent were concerned about heavy metals, while 59.3 per cent were concerned about chemicals. Some 52 per cent of respondents feared their drinking water may contain too many bacteria. At the request of New Forum, a Water Supplies Department lab tested about 30 samples from Kwun Tong and found a high content of iron. The average iron content in the samples was 4.4 milligrams per litre. 'Drinking high-iron water in the long run can result in health problems,' said New Forum member Cliff Tang Wing-chun. He added that the group had received nearly 20 complaints from Kwun Tong residents about drinking water in recent months. The Water Supplies Department said the WHO had not proposed any guideline value for iron. 'Under normal circumstances, humans suffer no harmful effect from drinking water with traces of dissolved iron,' it said.