The question of how much to water and how often has no single answer. It depends on weather conditions, soil composition and the plants themselves.
1.On a hot, sunny day in midsummer, the average lawn uses 125 gallons of water per 1,000 square feet. The same lawn on a cool, cloudy day uses as little as 10 gallons of water. Mature trees can use up to 15 gallons of water per hour on a hot day. Any plant exposed to hot sun, low humidity and strong winds will evaporate large amounts of water that must be replaced from the soil or it will die. Grass is particularly susceptible since 85% of its bulk is water.
2.A good drenching once or twice a week is better for your lawn than daily light sprinklings. Deep watering produces strong, deep root systems that can safely withstand drought. This requires a long, thorough soaking of the soil, ideally to a depth of about 1 foot but at least 6 to 8 inches. A steady stream of water will run off. An even, intermittent sprinkling is best for deep penetration.
3.Coarse, sandy soil has large air spaces that quickly fill with water but also lose water quickly to the subsoil requiring shorter, more frequent watering. Heavier clay or silt soil has numerous smaller spaces that absorb water slowly but hold more water than sandy soil. Clay soil should be watered slowly but less frequently. Loam-type soil falls in between, holding water longer than sandy soil but not as long as heavy clay soils.
Let the soil dry between watering. Roots will grow deeper, looking for water below the surface as soil dries. Roots need to absorb small amounts of oxygen from air spaces in dry soil and are warmed by the drying soil. This also discourages weeds, which are often shallow-rooted.
Light watering produces shallow roots in the upper few inches of soil that are subject to rapid drying. In addition, many weeds have shallow roots that thrive on moisture near the surface. Too-frequent watering produces wet areas susceptible to lawn diseases, insects and drown root damage.
If nature hasn't supplied water as rain, apply approximately 1 inch of water, (a general rule of thumb). This will give deep penetration of the soil to a depth of 6 to 8 inches. One inch of water or rain is equivalent to 623 gallons per 1,000 square feet. Water should be applied no faster than the soil is able to absorb it. If water begins to run off before 1 inch is applied, stop sprinkling until it's absorbed and then resume.