Blackwater - Sailors for the Sea


Sewage discharge from marine heads can cause significant damage to surrounding waters. Discover different ways to manage blackwater on your vessel and what regulations you may need to follow.

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What is blackwater and how does it affect aquatic environments?

Sewage discharge (also known as blackwater) contains pollutants including nutrients, metals, toxins and pathogens. Blackwater discharged from your boat can impair water quality, negatively affect aquatic ecosystems and increase risks to human health. 

The law

Under federal law, it is illegal to dump raw, untreated sewage into navigable U.S. waters, including coastal waters within 3 miles of shore and inland waters (lakes, reservoirs, rivers, etc.). A No Discharge Zone (NDZ) takes this law a step further and prohibits the discharge of both treated and untreated sewage into a designated body of water.

A NDZ is created if a state determines that a body of water either:

  • Requires greater environmental protection and there are adequate pumpout facilities available.
  • Has particular environmental importance (e.g. sensitive areas such as shellfish beds or coral reefs).
  • Or has drinking water intake zones.

It’s important to know the locations of any No Discharge Zones and pumpout stations in the areas where you are boating. The U.S. Environmental Protection Agency (EPA) provides a list of NDZs and pumpout facilities by state.

All boats in U.S. waters with permanently installed toilets are required by federal law to have a Marine Sanitation Device (MSD) onboard that either stores sewage until it can be transferred ashore, or treats sewage to reduce the coliform count to such low levels that discharged blackwater poses no public health hazard. 

What are your options for dealing with blackwater?

There are several ways to handle blackwater onboard your boat, including the following:

msd, marine sanitation device, boat toilets

1. Direct Discharge: If you are boating in locations that do not have waste pumpout facilities, try to discharge your waste overboard while underway in deep water away from beaches and anchorage sites. Pumping out your waste near shore is harmful to swimmers, snorkelers, divers, other recreational users, and those who eat the local fish and shellfish.

2. Portable or Composting Toilet: They don’t require installed water, power or holding tank, and are great for weekend trips. Check out Nature’s Head and Air Head Dry Toilet for composting options.

3. MSD Type III: For regions with adequate pumpout facilities, a holding tank connected between your head’s discharge and a through-deck pumpout fitting is simple, inexpensive to install and meets the requirements of the law.

4. MSD Type III with Optional Overboard Discharge: In addition to the deck pumpout fitting, a Y-valve can be placed after the holding tank, so sewage can be directly dumped overboard beyond the three-mile limit, if based in the US. Y-valve must be secured in the off position to prevent accidental discharge of untreated sewage.

5. MSD Type I: All of the waste is treated by maceration or chlorination before entering the holding tank or being directly dumped overboard. Offshore recreational boats generally use this type of MSD.

*There is a MSD Type II, which treats sewage through aerobic digestion. However, it is generally found on large commercial vessels.

Did you know?

  • Discharge from a single boat over one weekend contributes the same amount of bacterial pollution as the treated sewage from 10,000 people (California State Water Resources Control Board)!