Estimating How Much Water Landscapes Use

 When you estimate a plant’s water use, the plant must be growing all by itself. When plants are grown together the roots intermingle, their branches might intermingle creating shade and wind diversions, not only that but its water use is confused with any neighboring plants close by! When you estimate a landscape water use, use the total sum of all your plants. It will be a little high because of influences by plants nearby. This can be estimated by someone who knows plants and their water use. For a traditionally sized family of four, landscape water accounts for about 70% of your water bill.

When recording the water use of plants, they must be separated from other plants such as using this weighing lysimeter and hoisting the individual plants.

How many square feet is your total landscape? Your landscape size is your lot size minus the house, patio, driveway, sidewalks, and any other hardscape that would be difficult to remove. The problem is your monthly water bill comes, at best, in gallons of water. Landscapes vary in size. The size of your landscape is in square feet.

Water bills, like this one from Henderson, NV, lists the water use of an entire home lot. You must multiply this by  approximately 0.7 to get the actual water use of a landscape.

You must convert the gallons of water used by your landscape to the size of your landscape in square feet. The multiplier you needed is to convert a landscape from cubic feet to gallons. The magic number that does that is multiplying the square footage by 7.8. That is, 7.8 gallons fits into a one cubic foot spot. Two cubic feet contains (7.8 gallons x 2 cubic feet) 15.6 gallons for every 2 cubic feet.

The front landscape size is calculate from the total landscaped area, not including the driveway, sidewalk, or any so-called hardscaped area.

Any time your annual gallonage represents less than two feet of water covering your entire landscape, you are doing a very good job! That is less than two feet of water needed to water your landscape each year! When the landscape gallon totals less than 4 feet deep, you are doing an acceptable job. Six feet or more is unacceptable for desert landscapes.

For instance, let’s say your landscape area totals 2000 square feet. 

This size includes every possible spot a plant can be planted. Two feet of water covering this landscape area = 2000 x 2 x 7.8 = 31,200 gallons of irrigation water per year. That is very good.

Four feet of water covering your total landscape area = 2000 x 4 x 7.8 = 62,400 gallons of irrigation water per year. That is acceptable.

Six feet of water or more covering the total landscape area (2000 x 6 x 7.8 = 93,600 gallons of irrigation water per year) is unacceptable.