Bleaching powder (a mixture of calcium hypochlorite [Ca(OCl)2•4H2O], Basic Calcium Chloride [CaCl2 • Ca(OH)2 • H2O] and some free lime), which has about 35% available chlorine (grams of chlorine liberated from 100 grams of the sample when treated with dilute acid), is the cheapest and most widely used disinfectant in underdeveloped countries and in remote areas. On a small scale, it can be easily applied in the solid form. If to be used for small water works, a suitable amount is stirred in a known volume of soft water and the suspension is allowed to settle. The Supernatant liquid is then applied to water usually with a dosing equipment. The hypochlorite reacts with water producing HOCI which acts as disinfectant :

$Ca(OCl)_2 + 2 H_2O \rightarrow Ca(OH)_2 + 2 HOCI$