Household water treatment using sodium dichloroisocyanurate (NaDCC) tablets: a randomized, controlled trial to assess microbiological effectiveness in Bangladesh

We assessed the microbiologic effectiveness of sodium dichloroisocyanurate (NaDCC) tablets used on a routine basis at the household level by a vulnerable population. In a 4-month trial in Dhaka, Bangladesh, one half of the 100 participating households received NaDCC tablets and instructions on how to use the same; the other one half received a placebo and the same instructions. Monthly samples of stored drinking water from intervention households were significantly lower in thermotolerant coliforms (TTCs) than those of control households (geometric mean, 2.8 [95% CI: 2.2, 3.6] versus 604.1 [95% CI: 463.2, 787.9]; P < 0.0001). While 61.7% (116/188) of samples from the intervention households met World Health Organization (WHO) guidelines for 0 TTCs in drinking water, none of the 191 samples from control households met such a benchmark. Residual free chlorine in water samples suggested that householders consistently used the intervention, but 11.7% of samples exceeded the WHO guideline value of 5.0 mg/L, underscoring the need to ensure that tablet dose and vessel size are compatible.