Irrigation Case Study

An Eastsound Water member recently was shocked to receive an $800 water bill for service between May 20 and Aug 20. They had used 48,000 gallons over the past quarter, which they didn’t believe was possible. During the prior quarters, the account averaged less than 5000 gallons per quarter.

The average water use for a single-family home during this period is less than 15,000 gallons per quarter, and the bill is normally $141. This raised a number of questions which we’ll explore.

Why is this account using so much more water than a “normal” house? The answer was irrigation. Specifically not well-planned irrigation. Hopefully, this case study can help members avoid similar mistakes in the future.

How much water is actually required for irrigation? Most Orcas lawns are allowed to go dormant during the dry summers and green up when the rains return in October. But some folks desire green grass or enjoy growing a vegetable garden. While different plants require different amounts of water, the common rule of thumb is a Pacific NW lawn requires 1” of water per week to keep it from going dormant. Landscaping plants require only ½” per week and vegetable gardens about ¾” per week.   (

In the 48,000 gal/quarter case study the property had 3000 sq ft. of irrigation area, which is a mix of lawn, landscaping and garden vegetables. Assuming 1” of irrigation per week as the intended goal, 1” over 3000 sq ft is equal to 1870 gallons per week. (3000 sq ft divided by 12 in/ft = 250 cubic feet of water. 250 cubic feet x 7.481 gal/cubic ft = 1870 gal).

How does the actual water use compare to the irrigation needs? This chart from the member’s EYE ON WATER daily metering history shows the water use for the property in August. June and July were similar. The property is using roughly 1000 gallons of water every other day.

Looking into the EYE ON WATER hourly meter reading data shows that there is a major spike in water use between 5 a.m. and 7 a.m. This spike is roughly 1000 gallons, and it corresponds with the programming of the irrigation system.

An analysis of this water use pattern suggests that the irrigation system is using 3500 gallons per week. If only 1870 gallons of water was used for irrigation each week the monthly water use would be roughly 8000 gallons. The current irrigation programming is potentially over-watering by 7000 gallons per month.

What are the financial implications of having an intentional irrigation plan? For a quarterly billing, the excess irrigation use (7000 gal/mo) is roughly $400 of water that was not needed.

A normal residential water bill is $141/quarter. In this case study, if the irrigation was programmed to provide only the “recommended” water of 8000 gallons per month the bill would be in the area of $360 ($141 base + $220 surplus use).     Under the existing use pattern, the case study bill was $800. ($141 base + $660 surplus).

It is not uncommon for members to be surprised at what their irrigation use actually cost. Hopefully, this case study will help members make the best decisions regarding their water use. Irrigation is a major component of why water use spikes so significantly in the summer months.   Of course, there is no One Size fit All solution. Eastsound Water has designed the water system to accommodate this peak summer demand, and our rate structure is designed to recoup the “peaking costs” from those members who contribute to the peak demand on the system.

Recommendations from this Case Study

Learn more about the water demands of your landscaping, and plan your irrigation to its actual needs.

Use EYE ON WATER to monitor your summer water use. This will help avoid the “surprise” associated with water bills that come at the end of the summer billing quarters. Learn more about EYE ON WATER at

Ask your landscaping or irrigation contractor to calculate your true irrigation needs.

Learn how to program your irrigation timer yourself.

Get the most from your irrigation by applying it during the early morning hours. This allows the water to soak into the soil before being lost to evaporation. Most landscapers recommend heavier, less frequent watering.

When planning next year’s garden, consider developing a “Water Budget” component.