The most efficient way to water is using a drip system which is on a timer and which works at night, except in the winter. During the winter be sure to only water in the mornings. We all forget that the sprinkler is on, so either install a timer that will switch off the water, or set a timer on your phone or watch. A watering can is a sensible way to water newly planted seed or plants as you will then know exactly how much water you are giving the plants. Gardeners love to fleetingly water the top 2 cm of soil and this will evaporate very quickly.