A piston arrangement for a clean combustion engine, such as a hydrogen engine. The piston arrangement comprises a piston configured for reciprocal movement inside a cylinder having a cylinder wall, the piston having a piston head configured to face a first compartment with pressurized gas, a sealing arrangement comprising at least one sealing ring configured to be arranged to seal the piston to the cylinder wall and separating the first compartment from a second compartment, and a water channel extending from an interior of the piston to the sealing ring to provide water for lubricating the sealing ring. The piston head comprises a pumping element configured to be arranged to pressurize the water in the water channel by pressurised gas in the first compartment.