Grass is normally irrigated using pop-up sprinklers. At the height of summer grass in Britain requires about 25mm (1″) of water in a week. This can be applied over the seven nights or (as we believe) over as few nights as possible. However, if you have laid turf and the weather is hot and windy this could go up to 35mm.
This can be done (we advise) over multiple applications in one night. On each application it enables the water to work its way down into the root zone then during the period the system is not working, air is drawn down. The process is repeated till the water makes its way to just below the roots. We use as a guide one millimetre of water will wet one centimetre of root zone, but this does vary tremendously.
Also by watering every three or four days you save water because after the system has operated, the soil on the surface and grass leaves are wet and will dry out. Therefore, if you water every four days, this only happens every four days. In addition, watering every night means the surface is kept wet and therefore encourages moss / annual meadow grass (some classify it as a weed).
After watering grass it uses the water closer to the surface first and as time goes on uses the water deeper in the root zone. Then as the root zone dries out, the plant will drive its root deeper.
If you have established turf with long roots you could water every four days. If you have just laid turf and the weather is hot, you may have to water every four hours during the day to prevent the turf drying up. Then as the roots grow into the root zone, you can leave a longer time between watering.