Mercer Island urges residents to conserve water amid heat wave

Mercer Island is urging residents and businesses to conserve water for a second consecutive day amid an ongoing heat wave.

The city first made the urgent request Monday night, sharing that water use on the island had skyrocketed, depleting the city’s reservoirs faster than they can be refilled as temperatures have climbed. Water use had to be reduced in the next 24 hours, the city said, to avoid mandatory restrictions.

According to an announcement Tuesday afternoon, residents’ preservation tactics are resulting in a “considerable decrease” in water use. However, efforts to conserve water must continue to help the levels in the city’s reservoir tanks improve.

“Between midnight and 6:00am this morning, the Island consumed 787,000 gallons of water, with use peaking at 5,200 gallons per minute. This was a considerable decrease from the same period yesterday, where 1.2 million gallons were consumed, peaking at an unprecedented 7,000 gallons per minute,” the city said in a statement.

“Please continue conserving water to keep this trend going in the right direction.”

If water use continues at high rates, the reservoir level will fall below the “fireband,” or the amount needed for firefighting abilities, the city said. Reservoirs are considered full when they reach 29.5 feet, and the fireband is 19 feet. If the city draws down the reservoirs to the fireband level, it will “begin experiencing reduced pressure in parts of the water distribution system.”

“At this stage, the City’s ability to pressurize fire hydrants may be compromised. Yesterday, the reservoirs were drawing down and not recovering, which is why the City issued the urgent alert to conserve water,” the city said in Tuesday’s announcement.

A backup line that supplies Mercer Island’s reservoirs is only providing a maximum of 2,500 gallons per minute, the city said.

Mercer Island has relied on the backup line for months after a water-main leak in April put the main supply line out of service. The city in April had already warned its residents of a potential need for water conservation.

Repair to the supply pipeline is underway, and a new liner was installed at the end of June to address its leak, the city’s announcement stated.

“Work is underway now to connect the liner to the main pipe. Once that is done, the liner will be sanitized and brought back online. The current timeline to have the pipeline fully operational is the end of July,” the statement read.

To conserve water, the city asks all residents and businesses to: 

• Ensure automatic irrigation systems are turned off
• Talk with any landscaping providers about cutting water use
• Avoid doing laundry for the next two days
• Minimize shower water use
• Do not run sprinklers
• Water plants/yards as little as possible
• Let your lawn go dormant (brown)
• Do not wash vehicles
• Do not refill swimming pools or hot tubs
• Turn off water features, such as fountains

Seattle Public Utilities supplies the region, including Mercer Island, with water from the Cedar River Watershed and the Tolt River Watershed, both located in eastern King County.

Year-round, 26 cities and water districts rely on a limited supply of stored water from these two watersheds to meet most of the daily needs of the region, according to the agency. 

Water consumption from July 1-7 across the regional water system averaged approximately 166 million gallons per day. This amount is about 8 million gallons per day less than what was consumed during the same period last year, and 10 million gallons per day more than what was used on average during the same period over the years 2010-19, SPU said online. 

Despite high water use on Mercer Island, the agency “anticipates the regional water system will have sufficient water supply for people and fish this summer.”

The city is monitoring water use and will adjust its water conservation requests based on the usage data and the reservoir water levels, the announcement states.

“We are hoping that your continued hard work over the next few days will allow the reservoirs to continue refilling. If we do that, we will avoid mandatory water conservation measures,” the website said.