Guide
A Clean Water Supply on Your Boat
A canal boat carries 200-400 litres of fresh water in a tank, refilled at canalside taps. With sensible care it's perfectly drinkable; with neglect it becomes t
3 min read · Updated 2026-03-29
A Clean Water Supply on Your Boat
A canal boat carries 200-400 litres of fresh water in a tank, refilled at canalside taps. With sensible care it's perfectly drinkable; with neglect it becomes the source of stomach upsets and a steady plastic-y taste. This guide covers tank care, filtration, and the etiquette of refilling.
How the system works
Most narrowboats have:
- A fresh water tank (200-400 litres typical, often integrated into the bow steel)
- A 12V pressure pump (Shurflo or similar)
- Hot water from a calorifier (engine-heated, central-heating-heated, or shore-power immersion)
- An accumulator tank (smooths pump pulsing)
- A pressure switch
Water flows on demand when you turn a tap.
Filling up
Water points are common across the canal network: marked on canal guides, often near locks and major junctions. CRT taps usually have:
- A standpipe with a hose tap
- A standard threaded outlet (you bring your own hose)
- A tap key or padlock-and-key combo on some
Bring:
- A drinking-water-grade hose (blue or white food-grade, not garden hose)
- A hose reel for tidiness
- A standard threaded fitting and adapter
- A CRT water key (cheap from any chandler)
Don't use a generic green garden hose; they leach plasticisers and taste foul.
Tank cleanliness
The tank itself is usually steel (older boats) or plastic (newer). Either way, it needs occasional care:
- Drain and refill at least annually
- Inspect inside if there's a hatch (look for slime, sediment)
- Disinfect annually using a marine tank cleaner (Aquafresh, Aquatabs, or weak chlorine solution)
- Don't leave water sitting unused for months
A neglected tank grows biofilm (slimy bacterial coating) which gives the foul "boat water" taste.
Treatment options
For peace of mind:
- Tank treatment chemicals (Puriclean, Aquatabs): periodic disinfection
- Inline carbon filter at the tap: removes taste, smell, sediment
- UV sterilisation: rare but possible on liveaboards
- Bottled water for drinking only, tap water for everything else (simplest approach for occasional users)
A simple inline carbon filter under the kitchen sink, replaced every 6-12 months, transforms the taste and is the most cost-effective upgrade.
How long does a tank last?
Typical use:
- 2 adults cruising: 50-80 litres/day
- 4 adults cruising: 100-150 litres/day
- Liveaboard alone: 20-50 litres/day (with conscious use)
A 300-litre tank lasts 3-7 days for a couple, 2-3 days for four people. Top up every 2-3 days on a cruising trip.
Water-saving habits
- Short showers (2-3 minutes; wet, soap, rinse)
- Turn the tap off while brushing teeth
- Wash up in a bowl, not under running water
- Boil only the water you need
- Use a foot pump or inline restrictor on the kitchen tap
Hot water
Most narrowboats heat water via a calorifier:
- Engine-heated: runs hot water when the engine runs (always, when cruising)
- Central-heating-heated: heats whenever the diesel boiler runs
- Immersion-heated: electric heater for shore-power use
Calorifier capacity is typically 30-60 litres. Enough for two showers if hot, four if warm.
Greywater
Used water from sinks and showers - "greywater" - leaves the boat through small overboard skin fittings on most narrowboats. To minimise environmental impact:
- Use biodegradable, low-phosphate detergents
- Don't pour cooking fat down the sink (use a small jar instead)
- Strain the sink before draining
Black water (toilet) does not go overboard - cassette or pump-out tanks only.
Drinking the water
UK canalside taps supply mains water, which is drinkable. The journey from tap to your glass is the unknown:
- A clean tank, clean hose and good filter = drinkable
- A neglected tank or rough hose = strange taste, possible upset stomach
- Most experienced boaters drink the boat water happily once the tank has been maintained
If in doubt, bottled water for drinking, tank water for everything else.
A water checklist
- Drinking-water-grade hose
- CRT water key
- Tank disinfected annually
- Inline carbon filter installed
- Greywater detergents biodegradable
- Calorifier anode replaced every 3-5 years
- Pump filter checked monthly
- Drinking water source decided (tap vs bottled)
Conclusion
A boat tank with annual maintenance, a decent hose and an inline filter delivers clean, decent-tasting water. Skip the maintenance and you'll be living off the bottled stuff. The work is small; the comfort it adds is real.