Wednesday, 3 September 2014

Water Filtration Plant


During our time in Belgium we increasing found it difficult to find water without going into a marina which is not always practical when often they are set up for smaller cruisers.

I did some research and found it really wasn’t that difficult to make potable water from river of canal water although its not a cheap solution to the problem.

Since being in France we have found free water at very occasional places but all to often the systems on moorings along with the electrics are broken and disabled.

I have saved this blog post until the first time I have used the system and survived.

The system comprises in my case 7 stages of filtration and a submersible 240v water pump.

Adapted to Hozelock fittings

The pump is inside a large washable 100 micron filter bag providing the 1st stage of filtration.

The next 4 stages are 10” filter housings with reducing filter size, 50, 20, 5, 1 micron. 1 micron is 1/1000th of a mm

My assistant demonstrates Smile

This bank of filters were pretty unstable relaying on just the copper fittings to hold it together so to stabilise it and toughen it up I fitted it to some 18mm ply. The problem with this is each filter has 4 screw fixings and 1 pressure release valve (the red button on top).  All of these holes needed to be transferred accurately to the ply.

Masking tape template

Transferred to the ply and drilled

This is what the system looks like in operation. Obviously the pump is under the water at this stage.

UV filter is the black bit

The next stage of filtration is UV light. Read about it here. That’s how it works!  The model I chose is a 72w unit capable of a flow rate of 6000l and hour. This UV light sterilizer has a unique design which turbulates the water through a helix design, so the water does not just run through the UV but spins inside allowing the UV more exposure before the water comes back out from the outlet.  This combined with a 500l/h flow control valve I have in the system the water has maximum exposure to the UV light.

In the photo the water enters the filters through the hose on the left and exits to the tank on the right.

Once the water enters the tank its filtered to 1 micron and been exposed to massive UV radiation so is clear and sterile.  The bulk of water used is for domestic use of course but the danger is Legionella especially in the fine spry of a shower.  At this level of filtration we should be safe but an extra filter level is on the exit from the storage tank.  This is 0.5 of a micron activated carbon filter and will remove heavy metals.

The final filter is for the drinking water and was already installed on the boat.  Its a

Seagull IV

I have a TDS (Total Dissolved Solids) meter.  A recent sample of marina tap water was 240 p/p/m the water out of our drinking water tap today is 160 p/p/m

Yesterday I used it for the first time.  Obviously a quick look at the source water to see it is acceptable.  My test is would I swim in it and with Google Earth check to see you are not close down stream to a sewage farm or factory and their outfall pipe.  Not that this should be a problem but why do it if 5 miles downstream there is nothing?

I filled up with about 1500l of water which took just over 3 hours.  By the time it was done it was dark.  The UV filter has viewing windows to see the bulbs are working.


Last night I drank 2 pints of water. I’m pleased to say having drunk another couple during today I have no Delhi Belly.

The whole system is connected by Hozelock fittings so it can be easily broken down into smaller parts for storage.

The total cost of the system including the Seagull which was already here is about £650.00

Now apart from Diesel we can live completely off grid.  If it’s sunny we can go up to 3 days on solar without running the engine to charge the batteries.  Even then with propulsion which also makes electricity, hot water and heat the radiators as we go along we only use about 50L a week when we are on the move.


  1. This looks very user (and builder) friendly! Thank you for posting in such detail. How often will you have to change the filters and are they easily obtainable?

  2. The filters are very easy to get mail order a small stock is what I've done.

    As for changing them I really don't know yet. I would suspect maybe 2-3 times a year if we used it full time, and of course depending on the clarity of the source water.

  3. Hi,

    can you tell me exactly what UV filter you used?

    Kind regards,


    1. Yes James