The Care And Feeding Of Your Boat's Water Systems

By Tom Neale

Boating is all about water, inside and outside your boat. So, let's take a close look at the maintenance tasks you'll need to carry out in order to stay on top of all your water systems, with loads of tried-and-true tips to keep everything clean and functioning well.

Illustration of a boat's water systemsClick to enlarge.

SEAWATER WASHING (1) Seawater systems such as anchor washdown and dishwashing with a seawater foot pump (if you're in clean water and rinse well with fresh potable water) can conserve water. Bathing in saltwater frequently causes skin problems in many people if done often. A freshwater rinse helps.

DRINKING WATER PURITY (2, 6) when in question, can be improved by addition of a small amount of bleach. The Washington State Department of Health recommends approximately 1 teaspoon of household bleach with no perfumes, dyes, or other additives per 10 gallons of water. See also the Centers For Disease Control site ( If possible, agitate the water after the addition of bleach and then let it sit for an hour. Chlorine odor will dissipate after a day. Bleach may initially make the water to which it's added unclear because it's killed the "bugs." The water clears as these settle to the bottom. They ultimately should be flushed out. It's preferable and safer to add product manufactured for the purpose; camping stores are good sources. If you have questionable water purity and no way to remedy it, boil water before drinking. Drinking-water filters such as GE's FXUVC under-the-sink cartridge remove many impurities and greatly improve taste. A water system UV light, such as those used in some reverse-osmosis systems, can kill viruses.

AIR CONDITIONING & REFRIGERATION (3) Condensation drain trays should be occasionally inspected to clear any blockage in drain hoses, which should preferably drain overboard rather than into the bilge. If trays don't drain fully, they'll develop a musty odor that will be circulated by the air handler.

ICEMAKERS (4) should be left open and off when not being used for a few days or longer to avoid odor and mold. Often the incoming water line is behind the unit in an area warmed by the unit, which facilitates stagnation and odor, particularly in the filter that may be in that area. When in use, the ice bin should be dumped at least every few days to keep water flowing. Good ventilation helps.

BILGE WATER (5) Oil-absorbent pads in bilges under the engine and whenever there's oil-spill potential are critical. They must not interfere with the operation of a bilge-pump float switch. Always clean loose fuel and oils out of the bilge with an oilabsorbent pad, and discard appropriately. Proper bilge-pump installation is critical and will vary with different boats. The hose interior should be smooth, the water column in the hose should be no more than needed, and great care must be taken to avoid backflooding from the sea. Visual and audible alarms are crucial.

Illustration of a basic bilge pump schematicA basic bilge pump schematic.

SUMPS (7) such as those used for showers should be cleaned and flushed through regularly, even if the shower isn't often used.

THRU-HULLS (8) should be checked for obstruction every time you haul the boat and/or dive the bottom. Inspect them with a strong light while hauled, such as Streamlight's Junior LED. While in the water, you may need to carefully (so as to not damage hose and valve) work an old table knife or similar tool around inside the hole to clear it of barnacles and other obstructions. A carrot scraper makes a good tool for small holes. If the hole is covered by an external filter, this should be removed, when hauled, for painting inside, inspection, and cleaning.


from thru-hull openings. Sinks, heads, engines, air conditioners, refrigeration, bilge pumps, and other components utilize thru-hull openings and hoses. Regularly inspect and operate all thru-hull valves. Some valves periodically require disassembly and greasing or cleaning while the boat is hauled. You may need to close one quickly when a breach occurs in a water passage inside the boat. Regularly inspect all hoses and connections. Old or suspect hoses will deteriorate over time, and should be replaced. Eventually wire inserts will rust and harm inner and/or outer hose walls. Preferred hose clamps are AWAB brand or similar. Double the clamps and regularly inspect. Cheap hose clamps tend to rust and break. Use hose appropriate for the job, such as marine-sanitation hoses for heads. ABYC standards should be followed in these and all other aspects.

HOLDING TANK (9, 10, 11) Some chemicals added to holding tanks can harm the environment if spilled, either from the boat or from pumpout-disposal systems and system failures. Various companies market what they claim to be environmentally friendly holding-tank additives with varying degrees of effectiveness. Thetford offers a "green" holding-tank deodorant and Raritan offers its non-chemical KO and says it's safe for the environment. Some boaters install a Raritan Electro Scan MSD (see page 78) plumbed to treat and discharge overboard where it's legal, and treat and discharge into the holding tank at other times.

HEAD WATER (10) Regular addition of products such as Starbrite's Instant Fresh Toilet Treatment and Raritan CP help keep head water odorless and improve operation of the head. Petroleum-based products can harm valves, seals, and gaskets. Check manufacturer's recommendations. Regularly pouring white vinegar into the head and flushing will help diminish calcium buildup on inside walls of head plumbing. Raritan's CH is stated to be environmentally harmless and is specially formulated to remove heavy calcium buildup as well as prevent buildup if used regularly. Head discharge hoses should be specified for MSD use. Other types of hoses are usually more likely to develop calcium buildup, deposits, blockages, and odor permeation. Plumbing the head to flush with fresh water can reduce odor.

HOT WATER (12) Heaters require periodic flushing by squirting in clean dock water with a water hose under moderate pressure through a discharge port at top, squirting around inside as much as practical, and draining through open intake port at bottom. Some hot-water heaters have a zinc anode for cathodic protection. These should be checked once a year.

ANTI-SIPHON (13) loops and valves are needed in some hoses that exit under water to prevent water from siphoning into the boat. Whether anti-siphon valves and loops are used depends in part on the location of relevant components in the boat and whether they're below the waterline or could end up below the waterline. These components include heads, sinks, and engines and their raw-water intake and exhaust systems. As a precaution, when you're away from your boat, close the underwater seacocks.

POTABLE WATER TANK (14, 15, 16) should be treated periodically with a product such as Starbrite's Aqua Clean and Water Conditioner to remove odors, scale, and bad taste. Also, thoroughly flush tank with clean water and pressure nozzle. Drain from bottom if possible; if not, pump it out. Follow manufacturer directions when applying anything to drinking water. Follow instructions and warnings for cleaning additives, particularly with aluminum tanks. New tanks, especially fiberglass or plastic, may smell of the material of which they're made. Often, adding baking soda to the water will help, as well as with other odors later. The amount depends on the severity of the problem and volume of the tank. Clarity of water may vary with source, such as from wells, cisterns, public water works, and reverse osmosis. The latter source, if coupled with a UV light and maintained well, probably produces the best water.

SHOWER BAGS (17) Dark shower bags can be filled with rainwater, kept on deck, heated from the sun, and discourage extended showers. Occasionally clean bags and flush to prevent growth.

DRAINS AND SCUPPERS (18) Cockpits, side decks, and other areas of a boat normally have drains to rid the boat of rain and boarding seas. Test these regularly with a hose to be sure they're draining adequately. Leaves, plant material, dirt, and other debris can quickly obstruct them. Boats can sink if drains aren't kept clear. Clear them with a high-pressure hose nozzle or plunger.

JERRY JUGS (19) are used to ferry water from shore, and to store extra water. These should be light blue to designate that they're for water only. (Yellow is for diesel, red is for gasoline.) Be sure to label jerries as an extra precaution. Stored in the hot sun, water jerries can get moldy inside, even growing grasses. Clean jugs as needed. A good high-pressure hosing with clean dock water may suffice. 

Tom Neale is a key member of BoatUS Magazine's editorial tech team.

— Published: April/May 2012


1. Anchor/foredeck washdown with pressure pump and foot switch.

2. Galley sink. Filter for cleaner cold water. Drains above waterline at max heel.

3. Air conditioning drip tray drains overboard above waterline at max heel.

4. Icemaker door open when not used.

5. Bilge pump drain well above water line on max heel. Smooth inner lining to hose. Vented loop may be needed if drain is near or below water line at max heel.

6. Head sink w/ filter on cold water and drain above waterline at max heel.

7. Shower sump pumped overboard to discharge above water line at max heel.

8. All thru-hulls equipped w/ sea cocks. Note double hose clamps.

9. Holding tank vented w/ minimum bends for better airflow.

10. Head discharges to MSD Type 1 w/ Y valve.

11. Holding tank has pumpout hose and gravity discharge overboard where legal.

12. Water heater has anti-backflow valve to prevent expanding hot water from entering coldwater system. (This tank is shown lying on its side, an installation seen on some boats. Normally, hot-water tanks are upright.)

13. Anti-siphon loops and valves.

14. Potable water tank w/ fill and vent.

15. Potable water tank has sediment filter prior to pressure pump.

16. Accumulation tank diminishes pulsation.

17. Solar shower bag

18. Scuppers drain cockpit. Some boats need scuppers w/ hose to discharge.

19. Jerry jug


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