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Pollution Prevention - Carwash Fundraisers

How can a car wash pollute our creeks?

A car wash is a great way to have fun while raising funds for your school or community group. But did you know that if soapy water enters the storm drain system it will flow directly to the nearest creek? Soap (even if it is biodegradable) is a pollutant that can be harmful to fish and other aquatic life that depend on clean water for their survival. As well as soap, car wash water can carry pollutants such as dirt, oil, and other automotive fluids into our creeks.

Is it possible to host a car wash that doesn’t pollute creeks?

Yes, you just have to select a site where the wash water can be disposed of without it entering a storm drain. The County of Sonoma can help you determine if the site is appropriate and offer suggestions on how to dispose of the water.

How do I keep car wash water from entering the storm drain system?

There are several ways you can do this. Use your imagination and the ideas below to figure out what will work best.

  • Wash the cars in a place where the natural drainage pattern will route wash water into a vegetated area such as a lawn or vacant lot. Be sure to have the owner's permission if wash water is draining onto a neighboring property. You might be able to use sand bags, rolled towels, hoses, or other materials to divert the surface runoff to the vegetated area.
  • Another way is to seal off the storm drain, collect the water, and use a small sump pump to pump the water to either a vegetated area or into a clean out opening to the sanitary sewer

How do I seal off a storm drain?

Many parking lots have grated inlets placed in low areas. If the grate can be removed, remove it and place a sheet of heavy plastic over the inlet that extends beyond the edges. Replace the grate. Then put a heavy rubber mat or a lighter rubber mat with weights on it over the grate. Be sure to form a tight, waterproof seal that will keep all water out of the storm drain. If the grate cannot be removed place plastic sheeting and then rubber mats over the top of it. Rolled up towels can be placed around the edge of the mat to increase its water tightness.


Some parking lots drain through openings in the side of the curbs called catch basins. Catch basins can be sealed off with a sheet of heavy plastic topped with sand bags or other weights. Again, be sure the seal is tight before you start washing cars.


If the car wash site drains into the street and then into the storm drain, be aware that sealing storm drains in the street is not allowed. It can create a traffic hazard and also endanger those running the pump. You must use a catch basin on private property with the owners permission.

Where do I get a sump pump?

Sump pumps are available at equipment rental stores for $15 - $20 per day. (They are commonly used to remove water from basements.) Or perhaps someone in your group has a pump that they would be willing to lend.

Is any other equipment necessary?

You will need a hose to carry water from the pump to either the sanitary sewer clean out or the vegetated area. An extension cord will probably be needed along with a source of electricity. A broom may also be handy to sweep water towards the pump or to spread the water out so it will evaporate.

Does the pump need to be turned on all the time?

No. Some pumps will automatically turn on when the water level reaches a certain depth. Otherwise, someone has to be responsible to turn the pump on and off as water accumulates and is pumped away. A pump that is left running without water flowing through it to cool the motor can overheat and be damaged.

Once the car wash is over can soap residue harm creeks?

Yes, rain can wash the soap into the storm drain system where it can then pollute creeks. It is a good idea at the end of the car wash, while the storm drain seals are still in place, to thoroughly rinse down the wash area and properly dispose of the rinse water.

This all sounds pretty complicated. How can I be sure that our car wash is set up properly?

County of Sonoma staff is available to answer your questions and even tour the site with you. We can offer suggestions and help you determine the best way to keep wash water out of the storm drain system. Call the Storm Water Section at (707) 565-1900 for assistance.

Although every effort is made to provide complete and accurate information on this website, users are advised to contact appropriate Permit Sonoma staff before making project decisions. This may involve contacting more than one section within Permit Sonoma(e.g. Building, Plan Check, Zoning, Well & Septic, etc.) since each section implements specific codes or ordinances which may affect your project.
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