Washing your car may seem like a great way to beat the heat this summer while accomplishing something constructive on your to-do list. But you might want to think twice about the environmental impact before you park your car in the driveway and pull out your bucket, hose and old towels.

Even if you use a biodegradable cleaner, the soapy water that runs off your car when you hose it down not only contains detergent, but residue from automobile fluids like oil, gasoline and antifreeze. Each time you rinse your car, the contaminated water flows untreated directly into the stormwater system and eventually makes its way into streams and rivers. And, as the water runs out of your driveway and down the street toward the storm sewer, it also picks up other toxic substances, like fertilizers, petroleum deposits and surface paint from the pavement. Parking your car on a grassy area while you wash it may help some, but the toxins will end up in the groundwater eventually.

As an alternative, consider using a commercial carwash facility. Whether a conveyor type, self-service, in-bay automatic or custom hand-wash business, these establishments are required by the U.S. Environmental Protection Agency (EPA) to capture and route their wastewater to a treatment facility before the water can be discharged into the sanitary sewer.

Toxic residues aren’t the only reason to take your car to a commercial car wash. Rinsing your car at home with a garden hose can use as much as 10 to 15 gallons of water per minute, while professional car wash facilities can limit the water flow to as little as three to five gallons per minute. If you spend an hour in your driveway washing your car, you may have sent as much as 150 gallons of contaminated water directly down the drain. This is especially important in long summer dry spells.

So help the environment and save time: leave car washing to the professionals.