§ 96. Mr. R. Bell
asked the Minister of Housing and Local Government what proportion of chalk, either by weight or by volume, is present in London drinking water.
§ Mr. Marples
By chalk my hon. and learned Friend presumably means calcium240W bicarbonate, the form in which calcium carbonate is held in solution in water. The concentration in London drinking water varies with the source of the water, and to a certain extent with the time of the year, but generally it ranges between 160 and 250 parts per million by weight expressed as calcium carbonate.