The invention provides an object (10) that during use is at least partly submerged in water, the object (10) further comprising an anti-bio fouling system (200) comprising an UV emitting element (210), wherein the UV emitting element (210) comprises one or more light sources (220) and is configured to irradiate with UV radiation (221) during an irradiation stage one or more of (i) a part (111) of an external surface (11) of said object (10) and (ii) water adjacent to said part (111) of said external surface (11), wherein the object (10) is selected from the group consisting of a vessel (1) and an infrastructural object (15), wherein the object (10) further comprises a water switch (400), wherein the anti-bio fouling system (200) is configured to provide said UV radiation (221) to said part (111) in dependence of the water switch (400) being in physical contact with the water.
