I think there are health and safety exemptions for watering: nobody would expect footballers or egg-players to play on rock-hard ground, so watering is allowed, although there would be an expectation on clubs to do so responsibly.
That being said, with the drought order now in place, it gives suppliers more power to put blocks in place if water levels at reservoirs drop dangerously low.
edit: it'll be those in grass-roots football I feel sorry for as they won't be in a position to play on watered pitches.