WATER SUPPLY. 121 



the soil, yet in time a filter becomes fully charged with 

 the impurities and cannot act any longer. 



To be quite safe a well should be situated on the rising 

 side of a bed of impervious clay, or gravel based on clay, 

 [so that any soil drainage should be carried /row2 the well. 

 'To exclude surface water the upper part of the well 

 should be curbed with brick laid in hydraulic cement, 

 and the wall should be carried some inches aboye the 

 surface and then covered with a flat 'flagstone with a 

 small hole in it for the pipe of the pump to pass through. 

 The flange of the pump should be cemented to the stone, 

 so that nothing can gain access to the well. A mound 

 of clay beaten firmly and sodded over with ^rass should 

 be put around the well, to divert the rain water ; or a 

 large water-tight platform should be made around the 

 pump. 



Where there are neither springs nor wells, cisterns will 

 be found useful. With some precautions cistern water is 

 quite free from objection. The precautions to be ob- 

 served are to have the cistern on high ground and safe 

 from ingress of surface water, and to have an automatic 

 arrangement for diverting the flow from the roof at the 

 first part of the shower, which washes the filth from the 

 gutters. A surprisingly large quantity of waste matter 

 will gather on a roof in a short time. Atmospheric 

 dust, pollen from trees and plants, droppings of birds, 

 insects, small dead animals, and the wear of the roof 

 covering, all these are washed into the cistern with the 

 first part of the shower and make the water extremely 

 filthy. A cistern becomes in many cases a collection 

 of exceedingly injurious filth, which renders the water 

 wholly unfit for drink, and dangerously infects the milk. 



To avoid this, an arrangement is attached to the lead- 

 ing pipe from the roof, having two connecting pipes, one 

 to receive the first flow from the roof, and one to take 

 the clean water after the roof is washed off. These two 



