In my personal opinion lawns should never be watered. Water is a precious resourse and during a heat wave will soon be in short supply. For the water to have any benefit on the lawn you need to apply a LOT. A wee sprinkle will be completely wasted as it will just evaporate. Doing it in full sun will cause the water to evaporate even more quickly.

Terrible waste of water through evaporation and not good for plants - grass is, after all, lots of little plants, so try to do it when the sun is off the grass, either early morning, or late evening, if you must - the grass will recover when the rains return, probably with a bit of extra moss next spring, without your watering at all.

I agree that its a waste to water a lawn and would take hours to penetrate my clay to any real affect. I consider I have good lawns because of the care I give them and thats why after a draught they always recover. Do you really want to be the only very green lawn in a draught? I wouldnt as I do hate to waste water.

If you've no hose pipe ban, then only give it a sprinkling in the evening when the temperature has dropped and the water has time to settle in.

I've seen many really desiccated lawns recover. Watering a lawn requires a huge amount of water and just isn't good environmental practice. Do as Drc suggests and make sure your lawn is well cared for all year round.

Just think of the acres and acres of grass verges and parklands which never get watered,they always recover :)

Think the point's been made, guys - for all we know, Guest has a newly laid lawn, in which case, it will need to be watered.