Sodium hypochlorite dosage for household and emergency

Point-of-use (POU) water treatment with sodium hypochlorite (NaOCl) has been proven to reduce diarrheal disease in developing countries. However, program implementation is complicated by unclear free chlorine residual guidelines for POU water treatment and difficulties in determining appropriate dosage recommendations. The author presents evidence supporting proposed criteria for household water treatment for free chlorine residuals of < 2.0 mg/L 1 h after NaOCl addition and > 0.2 mg/L after 24 h of storage. In testing of 106 drinking water sources from 13 countries, free chlorine residual was measured for 24 h after treatment with different NaOCl doses. For most unchlorinated water (with turbidity < 10 ntu or from an improved source), the NaOCl dose necessary to meet the proposed criteria was 1.875 mg/L. For most unimproved sources with turbidity of 10–100 ntu, the required dose was 3.75 mg/L. POU chlorination is not recommended in waters with turbidity > 100 ntu. The article also discusses the applicability of POU water treatment with NaOCl to emergency water treatment.