This is one in a series of A Guide to Narrow Boat Problems.
Excess water in the engine bilges
Hose leak, weed hatch, hull leak or rain entering from above. Condensation could be a contributory factor.
Check that it is just water. More than an acceptably small amount of anti-freeze or diesel could indicate a different source of the leak.
Use bilge pump if necessary, finishing with a sponge. Check all hoses and replace where necessary. Tighten weed hatch and check gasket, replacing if necessary.
A hull leak is unlikely in a modern steel boat but would be very serious requiring professional and expensive work in a dry dock. Seek assistance.
If caused by rain from above, clear all drain holes and gutters, but otherwise seal any gaps around the access to the engine room leaving air vents free. A firmly secure tonneau (this one is from Canvasman) covering the stern should also eliminate rain in the bilges.
The bilge pump will not extract the final half inch of water, for which a sponge (and rubber gloves) will be necessary. Disposable nappies are also excellent for soaking up the last half inch. Accept that a small amount of water is likely to come into the engine bilge and mop it up from time to time.
Keep drain and gutters free of debris.
Check weed hatch and double check for tightness after use, replacing gasket if necessary.
Check bilge pump from time to time.If it is automatic it should switch on when it senses water ingress, but remember that this depends on battery power, so heavy rains could drain your battery unless you have a solar panel to top them up. Where possible, personal inspection is the best solution.
Ensure boat is fully winterised by draining water tanks and systems before the frost sets in.
Check anti-freeze too.
A thin mat in the bilges can soak up oily water and keep the engine compartment clearer.