Incidence of gastrointestinal illness amongst participants in a randomised controlled trial investigating the use of untreated rainwater for drinking

Background

Water shortages are necessitating the use of rainwater tanks as a domestic water source in developed countries. Many health authorities do not endorse rainwater for drinking due to the unknown potential for health risks.

Methods

A double-blinded randomized controlled trial was conducted in Adelaide, South Australia to determine if consumption of untreated rainwater contributed to community gastroenteritis. Either a sham or active water treatment unit was installed at households with participants recording incidence of illness in a health diary for 12 months. The primary outcome was highly credible gastroenteritis (HCG).

Results

There were 769 episodes of HCG during the study (0.77 episodes/person/year), with the adjusted incidence rate ratio of HCG for the active water treatment compared with the sham group being 1.03 [95% confidence interval (CI) 0.81 – 1.30, p = 0.83]. The HCG rate ratios for children under 10 [ratio = 1.03; 95% CI, 0.67 – 1.57] and persons 10 years and older [ratio = 1.10; 95% CI, 0.84 – 1.46], were not significantly different (p>0.05). Blinding of the participants was effective (index of 0.65, 95% CI 0.58 – 0.72). Water consumption data showed that there was no significant difference in the volume of water consumed between the two groups (p>0.05) and no dose response relationship with HCG was found.

Discussion

The results of this study suggest that consumption of untreated rainwater does not contribute significantly to community gastroenteritis. In addition, the success of blinding provides further evidence that interventions investigating water consumption and health can be conducted at the community level.