For the period September to December 1985, 1226 water contacts were recorded during 8 days of direct observation. Various activities were analysed in order to determine their responsibility in transmission. An index of exposure, allowing for duration of contact, body surface exposed and infectiousness of the water was calculated for each contact. Domestic contacts, primarily female, represented 62% of the observations but only 15% of total exposure. Conversely, contacts for recreational purposes mainly involved young boys and accounted for 14% of the observations and 70% of total exposure. Between 6 and 20 years of age the mean index of exposure by contact was higher in males than in females. Changing water contact behavior seems to be an unrealistic means of preventing transmission in the community studied. The most appropriate strategy of control would appear to be selective treatment of heavily infected individuals.