WATER FILTRATION. LI. 



following are comparative analyses of the solids in solution 

 in the water at such times: — 



Sodium Magnesium Magnesium Calcium Calcium Organic Total 

 Chloride Chloride Carbonate Carbonate Sulphate Matter Hardness 



After a flood ... 77*45 10*70 33*42 47*98 21*25 34*40 200 

 During drought 292*5 43*4 84*0 99*0 35*4 23*3 330 



The above quantities are parts per million. The chlorides, 

 carbonates, and sulphates dissolved in the water vary con- 

 siderably from time to time, both in relation to each other 

 and to the volume of water. 



Flood waters descend the valley of the Hunter rapidly 

 after rainfall on the catchment area, and within the space 

 of a few hours the river water will change from one extreme 

 to the other. When the river is in flood the water is too 

 turbid for use. To provide against such contingency a 

 storage reservoir has been formed in the vicinity of the 

 water works by constructing an earthen embankment across 

 the outlet of an old lagoon. This reservoir contains, when 

 full, a reserve supply of 170 million gallons of clear water 

 which is resorted to when the river water is turbid, and it 

 is replenished mainly by water pumped from the river at 

 suitable times and. by rainfall on its catchment area of 

 200 acres. 



The sludge — largely composed of decayed vegetation — 

 which lay in the bottom of the old lagoon, was not wholly 

 removed when the reservoir was formed, and is added to 

 by the death and decay of water weeds which grow luxuri- 

 antly in the reservoir. Endeavours have been made from 

 time to time to get rid of the wesds, and large quantities 

 have been removed, but fresh growths rapidly replace them. 

 The sludge has a deleterious action on the quality of the 

 water. During summer the water rises in temperature ; 

 when the cold of winter comes the surface layers are 

 chilled and sink and displace the bottom water. A vertical 

 circulation ensues which brings up the stagnant water 

 which has been lying in contact with the sludge, and a 



