In addition to thinking about water conservation when watering the garden, gardeners should also consider the health of their plants. Fortunately, the needs of plant health and water conservation actually coincide, and the same advice about watering holds true for people in drought areas as it does for those with plentiful water who merely want healthy plants. As a general rule, watering should be deep and infrequent, as this helps plants to establish a strong root system. However, the time of day that gardeners water the garden is also important.
I have found that the best time of day to water the garden is early morning, before the heat of the day has set in. This reduces the amount of water lost through evaporation, and also provides water for the plants to help them get through the heat of the day. Every few days, water the garden with a deep soaking of water in the early morning, and use drip irrigation, watering cans, or targeted hoses, rather than sprinklers and other devices which diffuse the water all over the garden. Sprinklers are inefficient, and they can also cause plant damage. As a rule of thumb, try to water the garden with one inch (two and a half centimeters) of water every week, through a combination of precipitation and watering.
Do not water the garden during the heat of the day, because the water will evaporate, rather than penetrating the soil. The goal is to deeply soak the soil, encouraging the plant to put out more roots to search for water, rather than creating a shallow area of moisture and keeping it moist. A plant with ready access to water through daily watering will develop a shallow root system and become weakened. Plants which are used to the stress of less frequent watering will also do better in varied weather conditions, or when a gardener forgets to water the garden.
If watering in the evening, after the heat is passed, make sure to water early enough that the leaves of the plants will completely dry before night time. Fungal infections can colonize leaves which are left moist overnight, and roots will also suffer from being watered in the late evening. Being left moist and cold at night can lead to rot and fungal infections of plant roots, an undesired result.
If you are trying to conserve water, water the garden with reclaimed water and rainwater, and make sure to check your irrigation system for leaks frequently. If you have time, hand-water all of the plants to ensure the most efficient use of water, checking the soil for moisture levels. If you do not, invest in a quality irrigation system which will help your garden to flourish. Gardeners with less water concerns should still water the garden wisely, as extra water will not lead to healthier plants.