When completed, water the new lawn every day for the first 2 weeks paying particular attention to the joints as these areas will dry out quickly and gaps will appear giving weed an opportunity to grow through.
As a guideline use a sprinkler to water an area for approximately 5 to 10 minutes twice a day, gradually reduce this so as to encourage the roots to look for a water source from below the surface which will aid with developing a strong root system quickly.
Depending on the weather reduce the watering to 2 to 4 times per week for the next few weeks. Once you get into the sixth week you can water weekly bearing in mind if the weather becomes very dry you should increase the watering again, for a period of up to 6 months.
Avoid laying turf in extreme heat.
It is essential not to over water your freshly laid turf as this can cause shallow rooting. Check that water has drained away and is not sitting on the surface underneath the turf as this may also cause the roots to rot so the turf will not establish.
Overwatering also encourages weed grasses such as annual meadow grass.