Black water gets all the attention. Holding tanks, pump-outs, the dramatic question of what happens when you flush. Grey water, the run-off from your galley sink, your shower and your washing-up, slips through quietly because it feels harmless. It is not. Whatever you pour down a boat drain at anchor goes straight into the water you are about to swim in, and over a busy summer in a popular bay the cumulative load is real. I changed the products in my lockers a few seasons ago and I have not looked back.
What the law actually requires
Start with the rules, because British sailors arriving in France often assume their home practice transfers. France treats sewage strictly. Boats built after 2008 and fitted with a toilet must carry a holding tank or an approved treatment system to enter a French port, marina, mooring or anchorage, and in exchange French ports are obliged to provide pump-out facilities. Treated black water may only be discharged beyond three nautical miles from shore, and the vessel must be making at least four knots while doing it. Discharge of waste water is banned outright in canals and rivers.
The teeth matter. A pleasure boat under 20 metres caught disposing of waste at sea where it should not can face fines up to 4,000 euros. That covers more than the obvious offence, so the safe assumption inshore is simple: nothing goes over the side in a harbour, an anchorage or close to a beach. If you want the full mechanics of tanks and pump-out fittings, I cover them in my guide to holding tanks and no-discharge in France.
Grey water sits in a greyer legal space, which is exactly why your own discipline matters. The regulations focus on black water and on treatment systems rather than on the chemistry of what you wash with, so nobody is going to fine you for the soap you choose. The marine life in the bay does not read the statute book, though, and it responds to phosphates and surfactants regardless of what the law says.
Why grey water is not innocent
Conventional washing-up liquid and shower gel carry surfactants and, in some products, phosphates. In open ocean these dilute to nothing. In an enclosed, slow-flushing bay full of anchored boats they build up. Phosphates feed algal blooms that strip oxygen from the water and smother the seabed habitats that keep a bay healthy in the first place, the same meadows and beds I write about in my notes on low-impact anchoring for wildlife. Surfactants strip the protective coating off fish gills and harm the smallest organisms at the base of the food chain.
None of this is catastrophic from one boat on one night. The point is that you are never the only boat. In August a single Riviera anchorage might hold sixty yachts, and if each one rinses the dinner plates with a phosphate-heavy detergent every evening, the bay carries the load of all of them at once.
The products that earn their locker space
Switching is cheap and the performance is fine. Look for a few things on the label:
- Phosphate-free, which has been the European norm for laundry detergents since 2013 and for dishwasher products since 2017, but is still worth checking on imported or specialist boat cleaners.
- Readily biodegradable, ideally certified to the EU Ecolabel, which sets limits on toxicity to aquatic life.
- Concentrated, because less product per wash means less going overboard and less weight to carry.
In practice I keep a single concentrated, phosphate-free washing-up liquid, a plant-based all-purpose cleaner, and a biodegradable body wash that doubles for hair. Vinegar handles descaling the kettle and the heads, bicarbonate of soda scrubs the galley, and between the two of them I have retired most of the aggressive chemical cleaners I used to stow. For the heads I avoid anything chlorine-based that ends up in a holding tank, since it kills the bacteria you want working in there.
A galley routine that keeps the bay clean
The product is half of it. The habit is the other half.
- Scrape plates into the bin, not the sink. Food waste fouls the water and clogs the pump.
- Wash up in a bowl rather than under running water, then carry the dirty bowl to a marina sink or shore facility when you can, rather than tipping it overboard at anchor.
- Use the minimum soap that does the job. Most of us use three times what we need out of habit.
- Save the big wash, hosing salt off the boat, scrubbing the cockpit, for the marina where the run-off goes into the drainage system rather than the anchorage.
- Shower ashore in the marina when you have the chance. A modern French marina almost always has decent showers, and it spares both your water tank and the bay.
That last point links to the wider economy of cruising. Water, power and showers are part of what you pay a marina for, and using them well is both greener and cheaper than running everything off the boat. I go into the detail of what French marinas provide in my notes on marina water, electricity and showers.
Shower water, sunscreen and the things you wash off
Grey water is not only the galley. The shower drain and the swim ladder carry their own load, and the worst offender is one most sailors never think about: sunscreen. Conventional sunscreens shed oxybenzone and octinoxate into the water, chemicals linked to coral and seagrass stress, and on a hot week in a busy bay a few dozen swimmers rinsing off adds up fast. Reef-safe mineral sunscreens based on zinc oxide do the same job without the same chemistry, and they are easy to find in French pharmacies and supermarkets. Switching is one of those changes that costs nothing and removes a genuine pollutant from the exact water you are swimming in.
The same logic applies to hair and body wash used in the cockpit shower. If you wash off salt with a bucket over the side at anchor, use the mildest biodegradable soap you have, or better, save the proper wash for the marina. A quick freshwater rinse with no soap at all is fine over the side and keeps the bay clean.
Watermakers, tanks and the temptation to over-wash
There is a habit worth naming. Boats with watermakers and generous tankage tend to use far more water, and therefore far more soap, than boats that have to ration it. The discipline of treating fresh water as finite, even when you have plenty, tends to cut your grey water output by itself. Wash up once a day rather than after every cup of tea, run a sink of rinse water rather than a running tap, and you produce less waste water of any kind, however clean the product.
The honest limits
I am not going to pretend a bottle of eco-friendly soap saves the Mediterranean. The largest pressures on these waters are agricultural run-off, plastic, and the sheer number of boats, and a sailor rinsing plates with greener detergent is a rounding error against all that. What it is, though, is the part you control completely, at almost no cost and no loss of comfort. It also tends to pull the rest of your habits into line. Once you are thinking about what goes over the side, you start scraping plates properly, carrying rubbish ashore, and using the marina facilities you are paying for anyway.
There is a quieter benefit too. A boat run on milder products simply smells better below decks, the bilge stays sweeter, and the water around the swim ladder stays clear enough to enjoy. The bay you anchor in tonight is the bay your kids snorkel in tomorrow morning. Treating the galley sink as if it drains straight into that water, because it does, is not zealotry. It is just paying attention to where you actually are.
