This is directly from John Garrett on the stadium tour. When asked why the pitch is watered so much.
The pitch is constantly lit, fed and cut, the water is just a delivery system for the food, we have a water tank (its in the brick structure under the Westfield corner) water is taken from the tank mixed with food and sprayed onto the pitch, it then drains back into the tank, we could water 24/7 and pitch would still not be over watered, perversely, when it rains the food is washed away so even more watering is required.