Plants like people need water for healthy growth and development. Gardeners often need to supplement rainfall to keep plants healthy. If done right, it can make the difference between a failed garden and success. Done wrong, it increases disease problems, causes greater drought stress for your plants and wastes water.
Water thoroughly, but less frequently. Established plants growing in clay soil need about an inch of water applied once a week. Those growing in sandy soils need one half an inch of water applied twice a week.
For best results water the garden in early morning. You lose less water to evaporation and reduce disease problems caused by having wet leaves at night.
Reduce the need to water by mulching the garden. A 2 to 3" layer of shredded leaves, evergreen needles or other organic matter will help keep the roots cool and moist. It also reduces weed problems.
A bit more information: Measure the amount of water applied by using a trowel to dig down 6 to 8 inches to see if the soil has been moistened. Note the position of the faucet handle and amount of time it took to do this. Now you know how long to run the soaker hose or sprinkler in order to apply the needed water to the garden.