How Much Water Does a Real Lawn Require?

After doing much research and taking advice from the professionals that look after lawns the following has been concluded.

Due to the sandy soil conditions here in Perth to maintain your lawn correctly, meaning that it is given enough water for the right amount of time so that; a) the roots grow to a correct depth to maintain continual access to water and b) grow strong and thick enough to stop the influx of weeds (have you noticed how many Perth lawns appear to have large clumps of weeds?  well this is why) . 

So to do this you would need to water your lawn enough that it receives 20mm of water three times a week.  So for a 50m lawn it would require 12,600lLitres of water a month during the hotter months.  With current watering restrictions this is legally impossible and on the Save 6 Buckets A Day campaign you would be saving over 46 buckets a day!