552 TROPICAL HYGIENE, SANITATION, ETC. 



The metal vessels used by the Hindus for water transport are certainly 

 an improvement on the mashak, especially as the metal tends to 

 sterilize the water. They can also be better cleaned. 



A pipe supply from a reservoir is preferable. For a reservoir a 

 valley could have a concrete or clay puddle and a dressed stone, 

 water-tight division thrown across it. Or an excavation could be 

 made. An overflow weir and an emptying pipe are essential. 



The points to watch before construction are : Suitability of site, 

 sufficiency of water supply, amount in gallons to be supplied per head 

 per diem, size of reservoir, number of days' supply to be stored, the 

 primary use of the reservoir, i.e., is it to be a quiescent settling basin 

 or preferably a continuous-flow settling basin ? 



Conveyance by means of pipes, galvanized and lined with pitch 

 or other anticorrosive substance is to be preferred to the open 

 channels. 



Airi vents will be needed at the summit, debris sluices below and 

 cleansing sections at intervals. 



Iron pipes become diminished in diameter owing to : — 



(i) Incrustations from oxidation w^hich can only be prevented by 



iseveral more layers of pitch on the inner side. 

 (2) Ferruginous slime in acid waters formed by germs and young 

 chlamydothrix which become attached to and grow rapidly 

 upon the inner linings. Alkaline waters and those containing 

 carbon dioxide are free from them. The Clarke softening 

 process is necessary, followed by efficient filtration. 

 (3) Debris in the irregularities of the water-main which can be 

 corrected bv brushing and rapid sluicing. 



WATER— PATHOLOGY. 



A pure sojt water acts upon zinc, e.g., on galvanized kettles, &c., 

 as a solvent so as to make the water injurious to health. Lead is also 

 dissolved by soft w^aters. Such water should be hardened with lime. 



There is no evidence that hard water is injurious. It does not 

 bring on old age neither does it cause gout, rheumatism, &c. 



Waters that are peaty owing to their acidity often dissolve lead 

 from the service pipes as lead carbonate. On standing or boiling 

 the lead carbonate is thrown out with calcium carbonate. 



Vegetable matter in solution or suspension, from any source, may, 

 if in sufficiency, cause diarrhoea. 



Animal matter in solution or suspension is always dangerous to 

 health, causing reduction in general bodily resistance, acute 

 alimentary disturbance, epidemic diarrhoea, dysentery, cholera, para- 

 sitic diseases and diseases of the typhoid group. 



