The study, commissioned by the Scottish Executive, was a follow-up to research three years ago which found that 15% of a sample of 661 recently built houses had tap water lead levels above 5 micrograms per litre (ENDS Report 311, p 12 ). This is higher than normally found in water supplies, and consistent with contamination from lead solder.
The follow-up looked in detail at 60 houses identified as containing lead-soldered water pipes in the first study. It found that lead solder could most reliably be detected in water samples by measuring concentrations in water allowed to stand overnight. Random sampling tended to underestimate the occurrence of lead solder by 50%, it concluded.
Applying these findings to the original survey, which used random samples, the best estimate of the proportion of new houses in Scotland containing lead solder must now be increased to 30%.
However, surveys by Scottish local authorities have found over 50% of new housing containing lead-soldered drinking water pipes. Applying SCIEH's findings to their results suggests that pipes in virtually all new housing in some areas may contain lead solder.
The study also looked at blood lead levels in residents of the affected houses. Although these were within normal limits, they were correlated with household water lead levels, and there was also a positive correlation between lead isotopes in blood and the solder.
The study concludes that solder-derived lead was being absorbed by the residents of the new homes.
The Scottish Office responded to the original report by increasing fines for the illegal use of lead solder. In England and Wales, the Drinking Water Inspectorate has maintained that routine quality surveys by water companies would have detected any significant use of lead solder - a response which has been treated with scepticism by SCIEH.
The DWI said it was unlikely to do any research into the situation in England and Wales because solder-free piping systems were increasingly being used.