The most important thing to consider when watering a lawn is how efficiently can you do it.
A lawn can stay in a great condition if you keep ahead of the weather, let's explain.
A good regular seasonal feed
Make sure you have given your lawn a good feed throughout the year, especially the spring and summer feeds. By doing this you'll have good levels of nitrogen in the root zone to help the grass recover when the time and weather is right.
Sharp lawn mower blades
Next make sure your cutting the lawn with a sharp lawn mower blade, by having a sharp blade (even on a rotary mower) you've got a better chance of a clean cut. A blunt blade will tear the grass, which will lead to die back or prolonged damage.
Apply wetting agents frequently
Get a wetting agent into the root zone, this we do via a spray application, typically it helps the watering get to the grass roots very effectively.
Own watering (irrigation) sprinkler that works
Watering a lawn, even a few minutes a day, with a good sprinkler will save hours and hours of slow watering. We would highly recommend the Gardena Premium full or part circle pulse sprinkler, it offers 5-12.5m spray coverage (depending on water pressure you put through the hose.
A little and often
If you do all the above 4 steps your watering will be very efficient, very effective and money saving in the long run.
5-10 mins water any area will see the lawn recover in hours.
One last note, try to not let the lawn dry out, if it starts to looked stressed (this can be seen as the lawn laying flat, looking shiny or going dark, get on with regular watering.