Monday, 6 August 2012

Rainwater collection for the shower.

Rain:  A source of free water?
When planning our extended cruise south we decided to avoid marina berths as much as possible, so one of our biggest concerns on leaving the UK was how long we could survive without going into them for water.
Our HT had two prismatic flexible tanks in the lower bows, each holding about 25 gallons.  The  portside feeds the galley cold (drinking) water via a carbon filter which keeps it tasting sweet,  while the starboard domestic tank feeds the heads cold, plus the feed for the domestic hot water cylinder, which in turn provides hot water for the galley sink and the shower and basin in the heads. The water is heated using a 2kW immersion heater when we have shorepower, the engine cooling system if we run an engine, or a 10sq ft solar panel on top of the wheelhouse if we are at anchor in direct sunlight.  This system gave us enough water for about ten days of careful use, and if we stopped having daily showers we could make it last for about 20 days, but the domestic water rarely lasted longer than that, although we never came close to running out of drinking water. 
Last year as I was watching crystal-clear rainwater pouring off Freya Frey’s decks in Millbrook, I wondered if there was an effective way of harvesting this natural resource, and came up with a design.  It consists of a set of deck fuel filler fittings strategically placed on the side decks, which feed a small collecting tank located in the starboard aftercabin.  An automatic bilge pump inside this tank pumps the water through a fine filter to remove any dirt and debris, and from there the water passes in a small bore pipe along the underside of the side deck to a 35 gallon triangular flexible tank in the starboard bow.  This then gravity feeds the domestic (non-drinking) water tank, via a shut off valve. 
Installing the collector fittings.   
I checked carefully where the water flowed on the decks, and identified a spot for the collectors just forward of the main bulkhead as the best place.  The fuel fillers used were equipped with a lip around three sides which makes them ideal.   They needed to be adapted to fit the pipework used below deck so the first stage was to bond an adaptor into place.
Fig 1 Deck fitting and Hep2O reducers for assembly
Hep2O, an industry-standard push-fit domestic water piping system, was used for all the water pipes on board, including bilge pumps.  I decided to use GRP sealed with Sikaflex to bond the adaptors in place, and the first step was to make a mould for the GRP, which was done using a small piece of commercial plastic packaging from the galley wastebin.  A felt tip pen was used to draw round the Hep2O fitting on the packaging, and this was then cut out with scissors,   

 Fig 2 The mould with the hole cut, ready for fitting

The mould was assembled onto the adaptor and some glass fibre repair paste prepared.  This was put into the mould, and the deck fitting pushed into the mould.  Excess pasted was smoothed and removed on the inside of the fitting using a teaspoon, and the past was allowed to set.  Once it had set, the mould was split and the excess glass fibre trimmed off with a Stanley knife. This is best done once the paste has set but not fully hardened.  Next, the joint was reinforced with more glass fibre paste and this was allowed to harden fully before being sanded, and then the joint was covered in a layer of Sikaflex to ensure it remained watertight.

Fig 3a. The mould assembled onto the adaptor.

3b. Glass fibre paste in the mould.
3c. The deck fitting pushed into the glass fibre.
3d. Excess GRP trimmed off when set.
3e. Reinforced with more glass fibre.
The location of the deck fittings meant that the pipes came down through the after part of the galley, and behind the nav station, before going aft through the starboard engine room to the collecting tank. 
Fig 4. Under the sidedeck in the galley showing the collector in place
The collectors were fitted onto the side decks using a hole saw to cut a circular hole, and then sealed with Sikaflex, leaving a small gap between the toe rail and the collector so that saltwater and dirt from the deck can be drained away before water collection starts.  Once the rain has rinsed any salt off the decks, a piece of kitchen roll is screwed up and then pushed into the gap to act as a dam, and the plugs are removed, lowing the water to enter the system. A small breakwater was also constructed using Sikaflex between the coachroof and the collectors to divert the water into them.  A small teastrainer element fits inside the collector, and this filters out the larger particles of grit and other debris which collect on the decks.
Fig 5. The collector on the sidedeck with the tea strainer and the kitchen roll plug in place.  The Sikaflex breakwater extends to the coachroof under the window
A couple of minor modifications were made on deck, which involved blocking off the first set of scuppers on each side to ensure that the rainwater stays on deck.  This was done with white UV resistant Sikaflex as a temporary measure.  I originally intended to do a permanent job with glassfibre, but the Sika has worked so well that I have never considered changing it.
Fig 6. The modification to the scuppers with Sikaflex
Another modification was to bond hardwood strips onto either side of the coachroof to ensure that water from the coachroof flows far enough forward to go into the collectors.  This was done using Sikaflex and stainless self-tappers, which were subsequently covered over and the wood painted with Toplac.
Fig 7. Hardwood strip on the coachroof to divert rain to the collector

The pump tank

The pump tank was made from a 5 litre airtight plastic clip-top food container from a local supermarket. 
A submersible bilge pump was screwed in the bottom of the tank using stainless nuts and bolts, along with a floatswitch.  An ordinary domestic tank fitting was used to feed the water from the deck collectors by gravity into the pump tank (bottom right fig 8), and a piece of polythene tube was used to connect the outlet of the pump to a through-bulkhead connector (top right) which leads to the filter.  The hole for the wiring was deliberately not sealed in order to provide a breather hole to prevent airlocks.   
Fig 8. The assembled pump tank, ready for fitting. Note that all electrical connections are made outside the tank.

Two battens were made and were screwed to the lid from the inside using stainless steel screws and large penny washers.  The battens were then attached to the inside of the aft hull void and the tank clipped onto the lid from underneath.  This makes for easy servicing to remove any dirt which gets past the deck filters.
Fig 9. The pump tank clipped in place showing the inlet (left), outlet upper right) and drain (lower right) pipes and the wiring loom (top right).
Fig 10 General view from above of the tank clipped into place, showing outlet pipe leading to the blue filter housing at the bottom.  The white stopcock on the right is a drain leading to the bilge, which is used to drain the tank down completely when the unit is serviced.
The filter is an off-the-shelf heavy-duty domestic type with replaceable filter elements.  I picked this up with a supply of about 20 elements for a fiver at a car boot sale.
Fig 11.  The filter body and a replaceable element. This screws into the blue housing at the bottom of fig 9.
The feed from the filter going forward to the flexible storage tank in the starboard forepeak was done in 10mm Hep20, as it is flexible and could be built into the underdeck insulation where it would be completely unobtrusive.  The storage tank has three connections:  a large bore filler on top, a 15mm breather (also on top) and a 15mm outlet on the bottom. 
The feed pipe from the filter housing was led forward under the sidedeck to the storage tank using  10mm Hep2O in order to reduce the amount of water which would siphon back into the pump tank when the pump switches off.  The pipe was led steadily upwards to ensure that the water would drain back to the pump tank thus preventing airlocks.  It was attached to a conventional deck fitting on the foredeck, drilled through just below deck level to accept the pipe, which was sealed into the fitting using Sikaflex.  An ordinary large bore reinforced hose fed the storage tank from the deck fitting.  This arrangement enables us to fill the tank whenever mains water is available, for example at a fuel berth.   The breather pipe fitted to the tank also serves as an overflow, and this is led at deck level into the starboard anchor chain locker.  
Fig 12. The deck fitting, showing the 10mm plastic feed pipe coming from the main filter
Does it work?
It is probably one of the most useful systems I have installed on the boat.   Rainwater is wonderful for showers, as very little soap is needed to get a lather.  There is practically no limescaling of the immersion heater, and no scum formed in the shower, so the inside surfaces of the heads stay cleaner for longer.  A decent shower of rain typically gives us between about 10 and 25 gallons of water.  A thunderstorm will often harvest twice that, so with the rainfall in Northern Spain we have gone for three months without needing to fill our domestic water tanks from the mains, in spite of each of us having a shower practically every day, as well as handwashing all of our laundry in the heads.  Obviously we only use the system in a sheltered anchorage or mooring, and the collectors are plugged off with screw caps before we put to sea, regardless of the forecast.   The system also provides us with a very useful reserve tank of water, which can be turned on when needed, and this  will give us greater endurance when we reach more arid areas. 
There is inevitably a certain amount of fine particulate matter which gets past the deck filters, and a small amount of this settles in the pump tank.  The rest is removed by the filter, and there is no sign of dirt in the storage tank.  The pump tank is cleaned out annually with warm soapy water, and the main filter is replaced at the same time.  The system is also sterilised from time to time by adding a capful of ordinary bleach to the deck fittings.
The most expensive part was the flexible tank, at £120.  Four deck fittings came to about £80, an automatic bilge pump another £40. The pump tank was about £10, and miscellaneous pipework and fittings about another £50, so all in all it cost around £300 to install.  Our water endurance between marinas is now much greater, which obviously cuts costs, if only in the diesel used to get to a tap, let alone marina berths.  Given that in France the marina showers were typically E2 each, being able to have two showers a day for 90 days at zero marginal cost has given us our money’s worth.



  1. This is an awesome design of rainwater collection. And nice installation too.

    Rainwater Collection


  2. Hey, nice site you have here! Keep up the excellent work!

    :Rain Water Harvesting