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recirculating grey water

My builder fortuituosly has provided two linked 450ltr water tanks in the bows.How practical can it be to dedicate one to collect bath and basin water to use for the two techma toilets using pumps etc?

Asked by: connol coan  | 4.25pm, Saturday 12 September

WW says:

You could collect the grey water to use flushing the toilet, but I can forsee a couple of problems.
Firstly, making sure that the grey water tank can in no way contaminate the drinking water supply- they would have to be totally isolated- a stopcock between them would not do.
Also, consider the implications for getting the water to the tank from the shower/basin. This would probably involve sumps and pumps.
When grey water is left in an enclosed tank, microbial activity will often generate some unpleasant odours. This means that whenever you flush the loo, you could be faced with a sulphurous smell coming back at you!
It might be easier to just use fresh water for the loo, and discharge the sink and shower in the usual way, directly overboard. Although grey water tanks are becoming more common in mainland Europe, they are designed either to be self-emptying (on faster flowing rivers) or for pumpout. This means that smell of contents, etc, won't matter.
Think about having to remove the clogs of hair and fluff from the tank as well (or from the filter to the pump(s) required to get the water from the sink to the storage tank)
Lastly, if the tanks are fitted to port and starboard, think of the difference in trim, if one is full and the other empty...

Mark Langley  | 9.57PM, Tuesday 15 September

Readers say:

Thank you Mark for that very comprehensuve answer.
On balance I will stick to the established use of fresh water to flush the loos

connol coan  | 10.11PM, Wednesday 30 September

We hired a boat in France that had a grey water holding tank. After about 3 days it was full and just overflowed into the canal. The smell was terrible. Far worse than the sea toilets that went straight overboard. Stale Grey water stinks

Brian Holt  | 11.50PM, Friday 23 October

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