Water Use Coefficient
Water use coefficient
What does coefficient mean?
Because water efficiency is required to win this contest, properties must meet a minimum water efficiency level to be judged. The H2Ownit Landscape Awards require all eligible properties to have a Water Use Coefficient
of less than 11.2 gal/sq ft.
To calculate your property's Water Use Coefficient
you'll need two pieces of information; your Outdoor Use Estimate
and your Outdoor Area Estimate.
We've included examples below to help you compute both of these numbers. Customers are encouraged to evaluate their property’s water efficiency prior to application. Properties that are ruled ineligible cannot be re-submitted for a full year after they fail the eligibility test.
How to determine your Water Use Coefficient:
There are several steps involved in calculating your Water Use Coefficient
and they are outlined for you here. Don't worry if it seems like a lot, we'll walk you through each step below!
Determine Total Water Usage
Add up all water usage for 12-month period being evaluated
Determine Outdoor Use Estimate
Subtract estimate for indoor water usage from Total Water Usage
Determine Outdoor Area Estimate
Subtract the Livable Square Footage from the Lot Square Footage
Compute Water Use Coefficient
Divide Outdoor Use Estimate by the Outdoor Area Estimate
The first step in calculating your Water Use Coefficient
is to determine your Total Water Usage,
which is the sum all your water usage for the 12-month period being evaluated.
You can do this by adding up the usage on all 12 of your last bills, or use the Pay or View Your Utility Bill
function through the City's web site to view your usage online:
Log in using your account number (If this is your first time logging in, you will need to begin by registering your account)
Once the basic account information pops up, select Consumption
from the purple menu on left.
Click on the water meter number to see charts with water usage for recent years.
Add up your water usage from the last 12 months to get your Total Water Usage
. Note that water usage is shown in thousands of gallons.
For this example, the Total Water Usage
is 101,000 gallons.
Use the Total Water Usage
to compute your Outdoor Use Estimate:
Our goal is to determine an estimate for outdoor water usage, so we have to subtract an average estimate for indoor water usage. For this contest, households are assumed to be efficient both indoors and out. The Average Efficient Indoor Water Use
(based on an average household size of 2.51 residents) is assumed to be 35,000 gallons.
Next, subtract the Average Efficient Indoor Water Use
of 35,000 gallons from your property's Total Water Usage
In this example, the household used 101,000 gallons in 12 months, making the Outdoor Use Estimate
Total Water Usage 101,000 gallons
Average Efficient Indoor Water Use 35,000 gallons
Outdoor Use Estimate
Determining your Outdoor Use Estimate
is the first half of the equation. Next, use the Maricopa County Assessor’s Residential Property
webpage, along with our example page to help you determine your Outdoor Area Estimate
. Once you've done that, continue on below.
Now that you have your Outdoor Use Estimate
and your Outdoor Area Estimate
, you're ready to calculate the Water Use Coefficient
for your property.
Using our example numbers, divide the Outdoor Use Estimate
for the past 12 months by the Outdoor Area Estimate
to determine the number of gallons used per square foot:
66,000 gallons / 4,710 sq ft = 14.01 gal/sq ft.
14.01 gal/sq ft is greater than 11.2 gal/sq ft. So this sample property is not efficient enough in its water use to be eligible for the contest.
If however, only 86,000 total gallons of water had been used here, the Outdoor Use Estimate
would have been 51,000 gallons.
51,000 gal / 4,710 sq ft = 10.8 gal/ sq ft.
With a Water Use Coefficient
of 10.8, the property would be eligible for the H2Ownit Landscape Awards.