36 WATER SUPPLY FOR DOMESTIC USE. 



rubbed together in hard water, which requires in proportion to 

 soft water a quantity of soap to produce a lather equal to the 

 degree of hardness of the water. A water of 10 degrees of 

 hardness (according to Clark's scale) means that it would waste 

 as much soap as 10 grains of chalk would if dissolved in 1 

 gallon of water. Every grain of chalk or degree of hardness 

 wastes about 8 grains of soap, which is not much in itself, but 

 in the water supply of a large city would mean a considerable 

 tax on its inhabitants. The city of Glasgow saved, from the 

 use of Loch Katrine water, £36,000 per annum in soap. The 

 extra cost in soap of a hard water over a soft water supply is 

 easily computed on the basis above mentioned. The average 

 quantity of water required for clothes washing and personal and 

 other washing, is 6 gallons per head daily. If the water sup- 

 plied contains 10 degrees of hardness and each degree of hardness 

 requires 8 grains of soap, the quantity required for each gallon 

 would be 80 grains, and for the 6 gallons 480 grains. This in 

 one year would represent 251bs. of soap for each person. The 

 price of this 25lbs. of soap, multiplied by the number of inhabi- 

 tants of a city would represent the extra cost of a hard water 

 over a soft water supply. Hard water is bad for cooking and 

 making tea. Clear, well aerated soft water is then decidedly 

 preferable to hard water for the reasons stated, but extra care 

 is required in the case of soft water to protect it from metallic 

 contamination, especially lead, on which it has a very salient 

 action. Hard water rapidly forms a deposit on the inside of 

 lead pipes, composed principally of lime salts in solution, which 

 protects the water from any contamination by the lead. No 

 lead piping should be used in connection with a rain water sup- 

 ply, and galvanised iron tanks should not be soldered on the 

 inside. Other metals are found in water beside lead, such as 

 iron, manganese, zinc, copper and arsenic. The two first are 

 unimportant ; copper is only met with in streams in the neigh- 

 bourhood of copper mines, and arsenic is seldom found in water 

 unless it gets there from the refuse of manufactures. The 

 extensive use of galvanised iron tanks imparts in some cases a 

 decided metallic taste to the water stored in them. Galvanised 

 iron is merely iron covered with a thin coating of zinc, put on 

 by galvanism. It is now becoming recognised that some cases 



