The film premeried in Cannes Un Certain Regard. Water Lilies follows three 15-year-old French girls who are discovering first love.
Slingshot had recently announced that it would branch out into distribution. The company acquired Water Liles from Films Distribution.
The Les Productions Balthazar production is also backed by the Centre National de la Cinematographie, Canal +, Region Ile de France and Arte/Cofinova3.
Slingshot MD Elizabeth Draper said: 'I am delighted we will be handling Water Lilies in the UK. It is a very special film and we are inspired by the opportunity to work with such a talented group of young people.'
Slingshot will launch its distribution business in August with the release of the company's first production, Gary Love's Sugarhouse, starring Ashley Walters, Steven Mackintosh and Andy Serkis.