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9601 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7608
Fax: 206.275.7814
Email: publicworks@mercer. . .
Hours: 7:30 AM - 4:00 PM (Mon-Fri)
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City of Mercer Island / Public Works / Emergency Well

Emergency Well

Emergency Well at Rotary Park
Emergency Well at Rotary Park

Emergency Preparedness is a priority for the City of Mercer Island.

The City is at risk in case of a major earthquake. In 2005, the Earthquake Engineering Research Institute and state emergency management officials released their report, “Scenario for a Magnitude 6.7 Earthquake on the Seattle Fault.” This report predicted widespread damage similar to the 1994 Northridge earthquake in California, and confirmed that Mercer Island should work toward the highest possible level of self-reliability. The conclusion – the City would make a sound investment by creating an emergency water source.
The City developed the emergency well to supply Island residents with water for an extended period of time without significant assistance from outside during an emergency.
The emergency well is not intended to relieve Island residents of the responsibility to be prepared in their homes, but rather to augment preparation at home. Even with the well, Island residents should still store their own three-day supply of water at home, setting aside one gallon of water per person per day.


In 2004, City staff assessed the Island’s water system and concluded that Mercer Island’s water supply from Seattle Public Utilities (SPU) would likely be disrupted in a disaster such as a major earthquake. Therefore, City officials decided to develop an emergency well that could be activated if the Island lost its supply from SPU.
Once a Feasibility Study was completed in December, 2005, the City selected a well site, applied for a drilling permit from the Department of Ecology and designed the test well. Test drilling began in 2007, and crews found a groundwater aquifer at a depth of more than 500 feet. Testing confirmed that the City could safely use this groundwater for an emergency water supply.
In August 2008, Mercer Island’s City Council approved the design for an above-ground permanent well facility. Construction was completed in spring, 2010.


Because of the Island’s unique geographic location and risk of being isolated by a major emergency, staff and the project team recognized early that “self-reliance” and “reliability” were the two top reasons for creating an emergency water supply.
After completing two extensive Water Supply Alternatives planning exercises, the project team concluded that establishing a groundwater well was the best alternative, ranking the well option highest of 15 alternatives that were explored. Other alternatives included withdrawing and treating water from Lake Washington, and adding more storage capacity.
The Emergency well is not designed to supply the Island’s water through its existing distribution system. The relatively small flows produced by the well are not hydraulically sufficient to move through miles of pipes and open pressure-reducing valves, and could serve only a small portion of the Island. In addition, permits do not allow it to be connected to the system.


Well operations are based on established strategies for emergency situations.
  • The well is operated under an Incident Command Strategy (ICS), which is designed to establish a consistent chain of command and clear roles that allow for solid decision-making, and maximize use of available resources.
  • Every detail of the well has been designed so that volunteers can activate and operate the well facility. Members of the Well Operations Team (comprised of more than 50 Island resident volunteers) have been trained to distribute water from the well and from trucks, dispatched to neighborhoods.
  • The well was designed for use with a back-up generator, since an emergency that disrupts the water supply could also cause power outages.


Water from the well will be available to residents on either a walk-up basis or in their neighborhoods, depending on conditions existing at the time.
Water will be distributed on-site at the well facility in six-quart collapsible containers. The City has stored thousands of these containers near the reservoir site. Mercer Island residents are also encouraged to pick up their own containers at the Utility Billing Counter of City Hall – one container for every household member.
In addition, 250-gallon totes will be transported by Well Operations Team volunteers with trucks into neighborhoods around the Island. This service will leave City crews available for other emergency response.


Water from the City of Mercer Island’s emergency well needs to be disinfected before it can be used for food preparation, drinking, or for hygiene purposes. This is a necessary precaution because unlike water from your tap, which is thoroughly disinfected before you receive it, water from this well is taken directly from a deep underground aquifer and has not been treated in any way. It is tested regularly and, unlike water from your tap, contains inorganic compounds such as manganese. As a result, it may look, taste and smell different.
Boiling in combination with chlorination is widely considered the best way to disinfect water. Boil vigorously for three minutes. You must let the water cool before you chlorinate it or the chlorine will not work. Regular household bleach is all you need. Do not use scented bleach or bleach with added cleaners. Add 16 drops of bleach (about 1/5 teaspoon) to a gallon of water, stir, and let it stand for 30 minutes. If the water doesn't have a bleach odor after this time, add another 16 drops and wait another 15 minutes. If the water still does not have a bleach odor after 15 minutes, the water is not suitable for consumption.
If your power is out, Well Operations Team volunteers will provide you with disinfecting tablets when you get water from the well. These tablets will help remove sediment and eliminate common micro-organisms such as harmful bacteria
For more information about water distribution and disinfection, see the Frequently Asked Questions and the Water Disinfection Information.

Emergency Preparedness is Still Your Responsibility

The emergency well was not designed to serve as your only source of water during an emergency situation. You are still responsible to be prepared with supplies in your home. We urge residents to store a three-day supply of water, with one gallon of water per person per day. Residents should change the stored tap water twice a year. Water is essential to survival, so take action now.

Additional Emergency Well Information

In Case of Emergency, Mercer Island Is Ready - New First-of-Its-Kind Emergency Well Now Operational
(News Release, September 23, 2010)

Mercer Island Breaks New Ground in Earthquake Preparedness with Emergency Well
(News Release, February 1, 2010)

Frequently Asked Questions About the City’s Emergency Well
Learn more about the well—how it works, who will operate it in an emergency, the safeguards the City took to protect the well from damage during a major earthquake and other information.
Water Disinfection Information
Water from the City of Mercer Island’s emergency well needs to be disinfected before it can be used for drinking, food preparation or for hygiene purposes. Boiling in combination with chlorination is widely considered to be the best way to disinfect water. This information provides easy, step-by-step instructions to treat water you get from the Emergency Well.
Seismic Stability/Vulnerability of New Groundwater Well, Mercer Island
This memo (dated March 1, 2010) summarizes the most important factors related to the seismic stability and vulnerability of the new Emergency Well. The memo was written by local seismic scientists and engineering experts:  Kathy Goetz Troost, LG (University of Washington), Burt Clothier, LHG (Robinson, Noble & Saltbush, Inc.), and Greg Hill, PE (Roth Hill LLC)


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