Water Conservation Guidance

Islanders can resume normal water use. Learn more here.

Because of our community’s hard work aggressively reducing water use over the past 48 hours, the City’s reservoirs have successfully refilled to adequate levels. We sincerely thank all Islanders for their diligence and help during this time.

Please continue conserving water to ensure we can maintain these levels. While we collectively curtailed enough water use to allow the reservoirs to recover from last weekend’s unprecedented demand, we need to ensure water demand does not once again overwhelm incoming supply while we are still operating on the backup supply line.

You’re likely ready to catch up on laundry, water thirsty plants, or take a real shower. Good news: it’s now safe to do so. However, please begin using additional water judiciously and ensure you’re following conservation steps outlined under the Voluntary Water Conservation stage:

• Water plants/yards no more than three times per week:
  • ODD numbered addresses water on Sun/Wed/Fri
  • EVEN numbered addresses water on Tues/Thurs/Sat
• Water early (before 10:00am) or late (after 8:00pm) in the day to reduce evaporation
• Let your lawn go dormant (brown)
• Postpone new planting until the fall when rain provides plenty of water for plant establishment
• Minimize vehicle washing
• Minimize refilling swimming pools and hot tubs
• Reduce shower time by two minutes
• Turn off water features, such as fountains

City staff are closely monitoring water use and reservoir levels. If water use once again begins to significantly exceed demand and reservoir levels drop, we will need to return to emergency water restrictions. We will continue providing updates on the status of our water system and you can monitor the City’s Water Usage Dashboard for real-time statistics.

Yesterday, the City pushed out urgent messaging asking the Mercer Island community to immediately reduce water use. This was due to declining water levels in the City’s reservoir tanks. Thank you for the fast response! The levels in the City’s reservoir tanks are improving, but we need to continue conserving water.

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

We know you have questions about how the City’s water system works and why these levels matter. Here’s what you need to know:

Why isn’t there enough water to meet demand?

The Island’s reservoirs are currently being fed by a backup water supply line that brings a maximum flow of 2,500 gallons per minute of water to the Island. Normally, the reservoirs hold enough water to meet high daytime demands and are then refilled overnight when demand is low. A combination of really hot weather and high demand, coupled with reduced supply, meant the reservoirs could not “recover” enough water overnight on Sunday, and reservoir storage levels started to drop.

Why do these levels matter?

The reservoirs must have enough water in them to supply adequate pressure and volume to meet community demand while also being resilient in an emergency. Critically important: the reservoirs must maintain high enough levels to ensure adequate fire suppression response. Mercer Island’s water infrastructure also supplies the fire suppression system in the I-90 tunnel.

To put this simply, our water reservoirs must have enough water in them to meet peak demand even if there was a major fire, a water main break, or another unexpected draw. For example, a water main break last year caused the reservoirs to drop two feet in two hours, draining more than 500,000 gallons. With incoming water limited to 2,500 gallons per minute right now, it would take multiple days to recover the water lost from that type of incident on top of high demand household and business water use.

There seems to be a lot of water in the reservoirs, though?

It’s important to understand what these levels actually mean. The reservoirs are considered full when they reach 29.5 feet. The “fireband” (the level below which the reservoirs may no longer provide enough water pressure for fire suppression) is about 19 feet. That means we can only draw down the reservoirs about 10 feet before we 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.

What should I do, and how can I help?

Keep conserving water! We have reduced water use significantly since yesterday and maintaining this reduction will help us refill the reservoirs to the maximum capacity overnight.

Please also help spread the word! Tell your friends and neighbors on the Island to make sure they’re aware.

How long do I need to keep this up?

City staff are carefully monitoring water use and will adjust water conservation requests based on usage data and the levels in our reservoirs. 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.

We will keep the community updated each day to let you know of progress and any changes. You can also monitor the City’s Water Usage Dashboard for real-time updates.

When will the main water supply pipeline be repaired?
The repair on the Seattle Public Utilities main water supply pipeline is currently underway. A new liner was installed at the end of June to address the leak. 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.

How can I stay informed?

All Islanders are encouraged to sign up for City emails, including urgent alerts.

You can also sign up for ALERT, the King County emergency alert system.

Stay updated on Let’s Talk.

Thank you for your continued efforts to help conserve water.

With warmer than average weather conditions, water use has spiked significantly on Mercer Island causing our reservoirs to be depleted faster than they can be refilled. All Island residents and businesses should conserve water immediately and cut unnecessary use.

Water use peaked at more than 6,000 gallons per minute over the weekend, significantly above normal peak consumption. Exceptionally high use has not subsided today.

Mercer Island is only receiving 2,500 gallons per minute from a backup line that’s supplying water to the Island’s reservoirs – this is the maximum amount of water this pipe can provide. Certain reservoir levels are required to meet water quality, safety, and fire suppression needs. If water use continues at these high rates, levels in the reservoirs will fall below the “fireband” which is the amount needed for firefighting abilities.

Water use must be adequately reduced in the next 24 hours to avoid mandatory water restrictions and prevent a severe water emergency.

We are asking all Island residents and businesses to conserve water now by taking new or additional actions, such as:

• 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

Additional water reduction measures can be found on the main Let's Talk water conservation page. You can monitor the City’s real-time water usage on our Water Usage Dashboard.

City Manager Jessi Bon and Mayor Salim Nice provided the community with an overview of this challenge and explained more about ways you can help in a Zoom Town Hall - you can watch the recording of the Town Hall webinar here: https://youtube.com/live/RBmcIHcJBuk.

Mercer Island is still facing a water shortage due to the Seattle Public Utilities (SPU) water supply line that is out of service. To ensure the City does not need to impose mandatory water restrictions, we are asking the Mercer Island community to make small changes in their daily lives to reduce water use.

We know many community members have started reducing water consumption at home, and the City is grateful for these efforts! However, the warm weather increases water consumption across the Island, and we all need to work together to keep our community safe.

If everyone makes one or two small changes, our collective efforts will help ensure the Fire Department has enough water supply to respond to emergencies this summer.

In addition to following general water conservation practices, the City is asking community members to take additional actions, such as:

• Water plants/yards no more than three times per week:
  • ODD numbered addresses water on Sun/Wed/Fri
  • EVEN numbered addresses water on Tues/Thurs/Sat
• Water early (before 10:00am) or late (after 8:00pm) in the day to reduce evaporation
• Let your lawn go dormant (brown)
• Postpone new planting until the fall when rain provides plenty of water for plant establishment
• Minimize vehicle washing
• Minimize refilling swimming pools and hot tubs
• Reduce shower time by two minutes
• Turn off water features, such as fountains

Additional water reduction measures can be found here.

You can monitor the City’s real-time water usage on our Water Usage Dashboard.

The City will keep the community updated about our progress and provide several days’ notice if water conservation guidance changes.

On May 1, 2024, the City Manager issued Proclamation No. 329 Declaring a Local Emergency due to the reduction in the supply of incoming potable water to Mercer Island caused by a leak in the Seattle Public Utilities (SPU) primary water supply pipeline to Mercer Island. SPU and City staff have been working to repair the primary water supply line, however given the highly technical nature of the repairs, work is not expected to be complete until late summer. The backup line will likely not supply enough water to keep up with the higher water demand typical during the summer months.

The City’s Water Shortage Contingency Plan (WSCP) provides guidelines to manage the water supply and consumption in the event of a water shortage. The plan enables the City to maintain essential public health and safety, and minimize adverse impacts on economic activity, environmental resources, and the City operations.

In June, the City anticipates activating the Voluntary Stage of water consumption reduction measures, as described in the WSCP. The WSCP identifies 28 actions that water customers can implement during the Voluntary Stage to significantly reduce water use – a combination of both behavior and hardware changes. The City hopes that by implementing these actions, entering the Mandatory Stage can be avoided.

Mercer Island City Council will receive a presentation of recommended actions in response to a water supply emergency at its regular hybrid meeting on June 4, 2024. Agenda materials for the meeting are available here (Agenda Item #11). The hybrid meeting will be broadcast live on MITV Channel 21 and live streamed on the City Council’s YouTube Channel.