Keeping students in school may not be as straightforward as providing them with clean water, but a filtered drinking supply makes them less likely to take sick days, research published on Friday shows.

The study, conducted by a UK-based medical school, compared drinking water access in eight Cambodian primary schools in Banteay Meanchey, Siem Reap and Battambang with the 3,250 students’ absentee records.

Students were 2.5 times more likely to attend regularly at the schools where French NGO 1001 Fountaines supplied filtered water, researchers found.

However, the difference in attendance at schools with and without clean water was noted only in the dry season.

“We believe that during the wet season, children may not always be able to get to school because of flooded roads, etc. or may be kept off school to help in the fields,” said Dr Paul Hunter, one of the study’s authors and a professor at the University of East Anglia.

At the schools that were not provided with drinking water, students predominantly brought their own water to class, or else drank from rainwater, public tube wells or from a nearby pond.

“Water and sanitation improvement at schools is critical to preventing students from getting sick from diarrheal diseases,” said Chay Lo, an author of the study and director of Teuk Saat, the local NGO arm of 1001 Fountaines.

UNICEF says 2,000 Cambodian children die from preventable diarrheal diseases annually.

The filtered water scheme costs $1.40 per student per day, or more than $4.3 million for all public school students, an amount the Ministry of Education said it can’t afford.

“The government budget can’t cover everything,” said Yung Kunthearith, deputy director of the school health department. Kunthearith was unable to supply data on absentee rates, but said 59 per cent of the nation’s 11,370 schools have clean drinking water.