148 



Hints on Water Supply. 



[JUNE, 



hardly be too large. It should really have a capacity equal 

 to one-fourth of the annual rainfall, estimated with reference to 

 the available roof area. Thus, assuming that the mean annual 

 rainfall of the district is 24 in. (2 ft.), and that the area of the 

 roofs to be " tapped " is 1,000 sq. ft, the service tank should 



be capable of holding _ I,OQ ° X 2 = 500 cub. ft., or (at 6 \ gallons 



per cub. ft.) 3,125, or, say, 3,200 gallons. 



House tanks and water-butts should be placed in situations 

 -where they will be protected against north-easterly winds in 

 the winter and, if possible, against the direct rays of the sun in 

 the summer. It is, perhaps, best to construct the service tank 

 T below ground, of brickwork set in cement and rendered inside 

 with neat cement, and to protect it by means of a stout wooden 

 cover fitted with a ventilating pipe and a flap-lifting manhole 

 cover ; but if a galvanised iron surface tank is used, it, too, 

 should be covered in and ventilated, and during the hot weather 

 limewhited on the outside so as to minimise the absorption of 

 heat. 



Existing wells should be gauged from week to week in order 

 that the available supply, at the known rate of consumption, 

 may be ascertained. This can be done by using a weighted cord, 

 which is carefully lowered until water level is reached (indicated 

 by the sound of the weight striking the water), when a knot is 

 tied in the cord, which is then further lowered until its sudden 

 slackening indicates that the bottom of the well has been reached ; 

 another knot is then tied and the cord withdrawn. The distance 

 between the two knots gives the depth of water in the well. 



A ready rule for arriving approximately at the number of 

 gallons per foot of water in the well, is to square the diameter of 

 the well, in inches, cut off one figure, and divide by 3. Thus : If 

 the well is 60 in. in diameter, 60 x 60 = 3,600 ; cut off one figure 

 = 360. This, divided by 3 gives 120, which is the number of 

 gallons for each foot of depth. If, therefore, the depth of water 

 were found to be 10 ft., the available supply in the well would be 

 1,200 gallons. As the bottom diameter of a well is sometimes 

 less than the top diameter, care must be taken, in ascertaining 

 the volume, as above, to adopt, for the purpose of calculation, 

 the diameter of the part where the water is : A lighted candle 



