780 million people lack access to an improved water source; approximately one in nine people.
3.41 million people die each year from water, sanitation and hygiene-related causes each year. An American taking a five-minute shower uses more water than the average person in a developing country slum uses for an entire day. The most critical issue facing the American West right now is a lack of water for human activities and irrigation. The Colorado river drains the south-west half of the U.S., it no longer flows into the ocean during the dry season because there is so much water diverted.
1.) Choose plants that are low water needs, or create shade in much of your yard. Xeriscaping makes use of succulents and stone landscaping to create beautiful yards with very low water requirements. If that's a bit extreme try picking out drought resistant varieties that will thrive in summer water restrictions. Plant water sensitive plants in shady spots.
2.) Mulch around plants to slow evaporation and discourage weeds. I personally prefer grass clipping and last year's leaves to make a tight dense mulch. Wood chip mulch is a good option for trees, but using it in your garden will lead to years of wood chunks mixed into your soil. Acid and alkaline loving plants may do well with pine needles or peat moss respectively.
3.) Use drip water systems, or hand water. Overhead water leads to loss by evaporation, and puts the water where the plant cannot use it. Where practical try to give water just to the roots of the plant, sprinkling a small area at the base. Drip water systems are the most practical way to water permanent landscaping like shrubs and perennial flowers.
4.) Water at night, infrequently and deeply. Plants actually use the most water at night. After collection solar energy all day, plants grow at night consuming water in the process. There is also less water loss to evaporation. Water deeply, but don't water every evening, give the soil a chance to dry out so that the plants are encouraged to grow large root systems searching for water.