How Much to Water

The answer to how much to water is ... it depends. Weather, sun exposure, slope, soil conditions and, most specifically, irrigation equipment affect how much to water. Sprinklers dispense water at very different rates. Learn more at a Water Wiser workshop with an opportunity to ask questions of our irrigation and conservation specialists.

  • Use the Run-Time Calculator to calculate a good estimate of how much water your landscape needs. This calculator uses our local, area weather stations. Keep in mind this is only an estimate, and a good place to start. You’ll need to monitor and adjust as needed. You may need to increase or decrease this estimate based on your observations.
  • Check your lawn by simply walking across it. If it springs back, the lawn does not need water. Another trick is to stick a screwdriver into the soil. If it is difficult to push in, the lawn probably needs water.
  • A good rule of thumb for turf grass is to water no more than 1.5 inches per week when the temperature is over 85 degrees. However, many yards now have a Texas Hybrid Bluegrass which uses 1/3 less water. Use a little less. If plants become dry and brittle, add a little more.
  • High traffic areas (from play and pets) and sunny spots will require more water than areas in the shade. For best results these areas should be on separate zones so they can be adjusted independently.
  • Cycle and soak, or watering in a quick series of short cycles, reduces runoff and more efficiently fills the root zone. This type of irrigation method is especially important for slopes and areas with clay soil. You’ll want to run each zone of irrigation and note how long it takes for ponding, pooling, or runoff to occur. When setting the controller, stop watering before you reach this point. Repeat as needed, with approximately 30 minutes between cycles, until the desired amount of water has been applied.
  • Replacing some turf areas with low-water-use plants and ornamental grasses adds variety to your yard and requires less water. Attend a ColoradoScape Design workshop to learn how. 

Calculating ET

The science behind how much to water!8 a.m. to 8 p.m. graph with wind, humidity, temperature and solar intensity

ET stands for evapotranspiration and is a measurement of the loss of moisture in the landscape through evaporation from the soil and transpiration from plant leaf surfaces. It is provided in inches per day. ET is determined by the following four factors:

  • Solar radiation
    Length of daylight hours and intensity of sun. Longer daylight hours, such as during the summer season, with little or no cloud cover increases water loss.
  • Temperature
    Higher temperatures result in higher water loss.
  • Wind
    Stronger winds result in higher water loss.
  • Humidity
    Lower humidity results in higher water loss.

Precipitation only replaces water lost and reduces the need for supplemental irrigation. Other factors, such as slope, soil conditions, and exposure must be considered when determining how much water to apply. 

Determining how much water to apply

For a typical residential landscape, add together all the ET values since you last watered - check out the historical data from our weather stations. For typical turf areas, multiply the total by 75%. This is the amount, in inches, that should be applied to nourish plants. For more native xeric areas, multiply the total by a much lower percentage.  Assuming the plants are established, start with 25% and adjust as needed based on your own site specific observations.

This ET value is standardized for an average cool season turf grass, such as Kentucky Bluegrass or a fescue blend. Many newer lawns are Texas Hybrid Bluegrass, that require 1/3 less water. There are also many warm season grasses like Buffalo Grass or Blue Grama Grass requiring even less.

Trees, shrubs, alternative turf types, and especially xeric plants may require significantly less water than the ET factor calculates. The key is to start small and work your way up. Let the plants tell you when they need water. All plants will show signs of stress. With native, xeric plants, too much water can be more harmful than too little water.

Learn more with our Run-Time Calculator.