Following are true regarding chlorination except -

Water to be chlorinated should not be turbid as it impedes the efficiency of chlorination. Chlorine demand for water should be estimated and free residual chlorine of 0.5mg/L should be present against subsequent water contamination. A contact period of ONE HOUR at least is essential for free residual chlorine to kill bacteria and viruses. No effect on spores, protozoal cysts, helminthic ova except in higher doses (PARK TB 25th edition pg 775)