Graywater

Water from onboard sinks, washers and showers is called graywater. Because boats are not connected to a permanent sanitary sewer system, graywater is discharged directly into the water without treatment. Graywater may contain nutrients such as phosphate and toxins including chlorine, inorganic salts and metals that can cause excessive unwanted algae and vegetation growth, decreases the dissolved oxygen in the water due to the decomposition of organic matter and contributes to a decline in water quality and the aquatic ecosystem. The discharge of graywater is prohibited in some harbors and marinas. Check with marina personnel for local restrictions.

Minimize Graywater Discharge

Use shore-side facilities - showers, sinks, laundry.
If not available, save showers, laundry, and dishwashing for home.
If possible, install holding tanks for graywater.
Use water saving devices such as low-pressure showerheads to conserve water.
Use more "elbow grease" and as little cleaning product as possible.
Use only biodegradable, non-phosphate, and less toxic laundry detergents, soaps, drain openers, cleaners etc.

Research your products before you buy them. Choose less toxic cleaning products, such as non-phosphate, biodegradable cleaners.
Look for products with official green certifications such as Environmental Protection Agency Safer Choice or Green Seal.

Try to skip the boat wash. Unless you need to rinse the salt water, wiping the boat down with a damp cloth will suffice.
Use tarps or canvas boat covers to keep boat clean between trips and reduce the amount of cleaning you need to do.
Conserve water and use water saving devices such as low volume showerheads.