Water system upgrade

Domestic Water Schematic

Water system modification and upgrade for our blue water cruise


Camomile was originally equipped with fresh water tanks capable of delivering 440 litres of water. She has two symmetrical stainless tanks which are located just forward of amidships under the saloon seating/bunks and these are linked together via a third smaller tank placed centrally and lower in the bilge. The feed for the water system is taken from this lower tank in order to enable a supply to be maintained even when the water supply is low and the boat is heavily heeled over.

The port side tank has a shut off valve which allows this tank to be isolated and therefore, if closed during a long passage for example, helps to protect the system from a total accidental loss of water due to a leak from the system. It can also helpfully provide water ballasting by shifting water to the “weather” tank if you feel the urge to squeeze out a bit of extra performance.

Overall we found that the system was fine all the while we were coastal cruising and able to fill up (practically) every day from a clean supply however for blue water cruising we had to make changes in three key areas.


Water making: For us, water makers fall in the same category as generators being amongst the most likely pieces of equipment to fail however, on balance we decided to fit a small modular unit which gives an output of around 17 litres per hour. The motor consumes around 17amps so we tend to use it when we are motoring and our experience so far has been that this easily maintains our drinking water supply. We also found that, despite a low intake location, tuning the routing of feed tubing and changing lift pumps, it really does not like operating in anything much above a slight sea because it tends to suck air into the system. This, the relatively low output of the unit and the power consumption means that it is not enough to supply our general water supply in all conditions. It particularly impacts when we visit places where, arriving with depleted tanks, the water supply is not good and the anchorage is not clean enough to run the water maker. Happily this has occurred very infrequently and separating the drinking water supply along with improving the capacity measurement has, so far, avoided limiting us.  


Drinking water purity: A dedicated and entirely independent 90 litre drinking water tank was installed complete with a manual foot pump to back up the electric pump. This tank is fabricated from food grade polyethylene with fittings and hose to match. It has a separate filler, vent and water maker feed. It also has a carbon filter close to the faucet which conditions the water to make it taste acceptable, something that the main tanks increasingly, on a 26 year old boat, did not do so well.

When we are in one of the many areas of the world where purity of water supply has a question mark over it the drinking water tank is filled and maintained exclusively from the water maker obviously taking measures to ensure that our intake of minerals normally found in the water is maintained.

So far this has been very successful as we are able to chemically treat our main tanks quite aggressively if we feel the supply has been tainted without affecting our drinking water. We have even been able to replenish our main tanks with the slightly brackish and completely undrinkable water which is sometimes found on low lying atolls when they have had a dry spell.

The strategy of separating the drinking water enables us save on our energy resources by running a smaller water maker less often as well as increasing our overall water capacity and adding another layer of safety to purity as well as its independence providing further protection against loosing our total supply through a leak.

An unexpected bonus is that when the watermaker membrane starts to fail and purity drops then the fresh water flush circuit (which takes the main tank water back through a carbon filter into the watermaker) can be diverted to feed the drinking water tank giving it a double scrub. This results in product water with a greatly reduced total dissolved solids reading meaning that even a failing membrane can continue to produce good water to drink. As even a failing membrane seems to produce water that is more than good enough for washing and cooking plus the product water flow rate increases substantially, thereby giving more litres per amp hour, it makes you wonder why a system could not be designed to operate like this in the first place.

Sea Water Our galley sink is fitted with a small sea water tap which, even though we have the watermaker supply is very useful in clean seawater areas for rinsing fruit and veg of all its resident wildlife and grime and for a first rinse on laundry day. The saving on our precious freshwater is significant at times however the motivation for fitting it was really to ensure that we had an alternative seacock for the engine raw water intake in case of blockages (2 happened so far) but also the ability to pressure feed the raw water cooling system should it’s impeller pump fail. The hose fitting on the sink can be quickly lead to the engine bay and connected to the intake circuit to enable operation to continue at low to mid revs.

Having seawater, washing water and drinking water options all available in the galley supported by separate circuits may sound complex but it is easy to live with and provides a level of redundancy which has proved indispensable in far flung places where resolving plumbing failures can be almost impossible. 

Water measurement: If you can’t measure it you can’t manage it. Never truer than with your supply of fresh water. Camomile originally had no means in place to check the amount of water in the main tanks and a small Zig gauge I had added to the port tank some years ago was both unreliable and inaccurate.

Our drinking water tank is easy to access, translucent and therefore can be easily monitored however the main tanks can’t be managed in this way being opaque and inaccessible. The best system I had come across was on a Amel where a sort of floating dipstick is located by the companionway but, although simple, I realised that any system would be only be completely accurate when the boat is upright and still.

I therefore installed a transparent sight tube on a level with the tanks, fed from the lower central tank, and a manual valved vent above it to allow it to breathe. The vent is fed as high as possible under the galley worktop and then returned down to the strum box to dispose of any leakage, the only drawback being that, under certain conditions, it is possible to cause a siphon and therefore a small puncture is required in the tube along with diligent closing of the valve which ideally would be spring loaded.

As our main tanks are not uniform in cross section the capacity scale for the sight tube would not have regular, even graduation so the scale was calibrated by emptying the tank 20 litres at time and marking the increments accordingly.

Even at sea this system can be made to work quite accurately if the heel is taken off and the vent valve is opened when the boat/tank is in its most neutral position.

Knowing the quantity of water in the tanks has been a real boon, allowing us to choose to carry less water (weight) on some passages but more importantly to be much more relaxed about how long we stay in some of the more remote anchorages where obtaining fresh water is an issue.


When we are cruising/anchoring our consumption runs at around 40 litres/day and we use our main tanks for washing/showering, washing up, cooking and cleaning but do not do laundry on board unless it is washed mainly with seawater and as Camomile has no salt water faucet this is not really very practical.

On long passages in hot climates we wash ourselves in seawater from a bucket on the boarding platform and then rinse ourselves off in fresh water from the transom shower. This may sound rudimentary but with air temperatures well into the 30s it is very refreshing and you can do it pretty well as much as you like.

We also have a 3m x 4.5m PVC sun canopy which is rigged at when anchor if we are not expecting severe winds. This can be fitted with funnels and tubes which divert any rain into the main tanks which can be quite effective in tropical downpours. In fact the main tanks were once filled in just over an hour on one of the outlying Fijian islands thus avoiding any water maker use at all during our stay there.

40 litres worth of rigid jerry cans are also carried on board which along with our stock of bottled water form our final backstop emergency stock and fresh water “grab bag” supply. We have frequently used our additional 150 ltrs of flexible jerry cans for topping up the main tanks by shuttling to a trusted dockside supply in the dinghy and this served us well in New Zealand and Australia where chlorinated supply is plentiful nearby to a lot of good anchorages but, particularly in Australia, marinas are expensive to visit.

Before the modifications to the original system were started the plumbing circuit was schemed out (drawing in ms excel) and although this took some time it was really useful. It not only helped to avoid mistakes (easy with so many tubes that looked very similar) but formed the basis of getting the right parts, length of tube and preparing locations for the major components whose relationship to each other within the hull is sometimes critical. The file was later extended to include all the boat plumbing and is used as reference when troubleshooting or making changes to the system.


  1. That is genius Kins, I can’t wait to see it on operation!

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