Drinking rainwater: a double-blinded, randomized controlled study of water treatment filters and gastroenteritis incidence

Abstract

Objectives: We examined whether drinking untreated rainwater, a practice that is on the rise in developed countries because of water shortages, contributes to community gastroenteritis incidence.

Methods: We conducted a double-blinded, randomized controlled trial in Adelaide, Australia. Sham or active water treatment units were installed, and participants recorded incidences of illness in a health diary for 12 months. The primary outcome was highly credible gastroenteritis (HCG; characterized by a specified number of loose stools or vomiting alone or in combination with abdominal pain or nausea in a 24-hour period), and we used generalized estimating equations to account for correlations between numbers of HCG events for individuals in the same family.

Results: Participants reported 769 episodes during the study (0.77 episodes/person/year), with an HCG incidence rate ratio (active vs sham) of 1.05 (95% confidence interval [CI] = 0.82, 1.33). Blinding of the participants was effective (index = 0.65; 95% CI = 0.58, 0.72).

Conclusions: Our results suggest that consumption of untreated rainwater does not contribute appreciably to community gastroenteritis. However, our findings may not be generalizable to susceptible and immunocompromised persons because these groups were specifically excluded from the study.

FIGURE 1

Rate of highly credible gastroenteritis (HCG; cases/person/year; 8-week moving average) during the study period (2007–2008) among participants with active and sham water treatment units (WTUs): Adelaide and Mount Barker, Australia, 2007. Note. Data collection was suspended for 5 weeks during the Christmas holiday period (December 17—January 20). The Christmas holiday period occurred at week 20, 24, or 28 of the study, depending on the start dates of the 3 batches of participants.