Water is a limited resource everywhere. Though the eastern half of the United States typically receives enough (or sometimes too much) precipitation, droughts do occur, and parts of this area sometimes go for several years without enough water to meet the needs of the local population. Most low-elevation areas of the western United States have low rainfall rates and a long dry season--and though the overall western water supply remains virtually fixed, ever more people are putting demands on it. Thus, conserving water is (or should be) a concern everywhere. Here are a few tips for waterwise gardening.

Locate plants wisely. Group plants with similar water needs together. They can then be irrigated together, and no plant will receive too much or too little water. This concept is called hydrozoning. To cut water use on plants that need regular moisture, site the "thirsty" individuals in a spot shielded from drying summer winds.

Reconsider your lawn. Of all the components of a typical garden, the lawn consumes the most water per square foot. Consider eliminating it entirely and replacing it with unthirsty ground covers such as juniper, coyote brush (Baccharis), or ivy (Hedera). Or install gravel, a hard surface like brick, other paving, or a wooden deck. If you don't want to part with your lawn completely, consider minimizing its size. When planting a lawn, choose a grass or grass blend adapted to your climate.

Mulch your plantings. An organic mulch spread several inches thick over the soil acts as an insulating blanket, slowing evaporation from the soil and keeping it cooler than it would be if unprotected. Rocks and gravel also do the job. Black plastic sheeting, sold in rolls, conserves moisture and suppresses weeds. You can also buy rolls of various plastic materials known collectively as landscape fabrics. Permeable to water and air, these are manufactured expressly for use as a mulch.

Eliminate runoff. Don't waste water by irrigating paved surfaces. If your sprinkler system showers water over sidewalks, patios, or driveways, replace the heads with a model that delivers water where it is needed. Or redesign the system.

Sloping land and heavy clay soils invite runoff--due to gravity in the first case, due to slow water penetration in the second. To solve the problem, adjust the rate at which water is applied. If you use sprinklers, you can improve penetration by watering in several successive short intervals, allowing time for water to soak in between each spell of sprinkling. Terraces and basins can also help prevent runoff on slopes; see above.

Use low-volume watering devices. Soil soaker hoses are effective and easy to install. Drip irrigation offers an excellent way to reduce water use. You can also upgrade an existing underground sprinkler system by installing low-volume sprinkler heads; or convert it entirely to a drip system, using parts and kits available at hardware stores.

Use timers. With the simplest timers, you set the dial for the length of time you want the water to run or the number of gallons of water you want to apply; then you turn on the water. The timer turns off the faucet for you.

More sophisticated timers operate on batteries or household current. You set them to a schedule; they turn the water on and off as programmed. Such timers assure that your garden will be watered whether you're at home or away. What's more, you can select a schedule that will give your plants no less and no more water than they need to thrive.

The flaw of automatic controllers is that they follow your schedule regardless of weather: they'll turn on the water during a deluge or apply amounts of water appropriate for hot summer temperatures on a cool fall day. To solve this problem, reset the controller to take seasonal rainfall and weather conditions into account. Or use electronic attachments that function as weather sensors. By linking a soil moisture sensor to the controller, for example, you can trigger the sprinklers to turn on only when the sensor indicates that soil moisture has dropped to the point where water is needed. Another useful attachment is a rain shutoff device; it accumulates rainwater in a special collector pan, turning off the controller when the pan is filled to a prescribed depth and triggering it to resume watering when the collected water has evaporated. Before installing either of these sensors, be sure they are compatible with your controller.

Conserve water on slopes. Plants on slopes are often challenging to irrigate, since water can run downhill faster than it can seep into the root zone. To prevent wasteful runoff, make basins or terracing to channel water directly to plant roots, as shown below.