Many plants in a small area can be competing within the soil to pull out enough water for themselves. This water competition can be severe. Remove excess plant competition from around any tree to decrease water stress. Use mulch to conserve water and to prevent weed competition. Careful application of herbicides can also reduce weed competition for water.
Gray water is waste water from the bath tub, shower, sink, dishwasher, or washing machines.
You may check to see if it is legal in your county or city. Gray water will plan a greater role in water conservation in the future. Xeriscaping, or developing water-efficient landscape, is becoming more important.