Water - Rain Harvesting and Filters

Rainwater harvesting

It’s possible to collect a lot of rainwater from even a small narrowboat roof and other collection methods can be tried on different kinds of boat or on near-by land.

There seem to be four main steps to rainwater harvesting, depending on what you want to use the water for: collecting, filtering, storing and purifying.

Water for a garden for example, won’t need purifying and you might not even bother filtering it. On the other hand, if you want to drink it, it’s a good idea to follow a very thorough process to stay in good health. You can store the water in portable clear containers if it’s going to be used within a day or two, but will need a different method if it’s going to hang around for a few days.

This is just one account of what I did on my own boat, with the aim of using rainwater for washing and drinking. I still fill up at BW water points when I find one, but otherwise use rainwater in my main tank.


If your boat has roof gunnels, the easiest way of collecting water is to block up any drainage holes along their length and allow the rainwater to run naturally towards the back of the boat and down into the stern. It can be funnelled down into a container and you could use one or both gunnels. I saw a boat with a funnel made from those 5 litre square plastic water bottles, cut off and inverted to fit flat against the boat.

My own boat has a lot of mucky things on the roof: earth in planters, logs, rusting trolley, etc and I find the gunnels are always full of sludge. I also travel about so having water containers on a small back deck wasn’t right for me. As my goal was to store rainwater in my main tank, I also didn’t want to be carrying full 20 litre containers round to the front every couple of days. So, I rigged up a separate collecting ‘roof’ that slopes forwards instead of back, covering 50square feet. (5ft wide, 10ft long)

It’s made from a very long palette as the base, a wooden structure hinged at the front (can be raised or flattened to go through low tunnels), a collecting surface (in this case, corrugated plastic sheets) and guttering. The palette, wood and guttering was skipped but I’m sorry to say I bought the corrugated plastic sheets after several frustrating experiments with other materials. I found that tarpaulin-type surfaces billowed in strong winds and allowed water to puddle rather than run. The material is also hard to keep clean and gets grimy quickly. Glass is good but I couldn’t get hold of big enough surfaces. If you can find them and can carry a couple of disused ‘french window’ type doors to your boat, I reckon they’d be great. Also, a tarpaulin stretched flat over boards would probably work ok too (I didn’t think of this at the time!) If I had some land, I’d like to try layered bark or shingles.


I have about 4/5 basic filters along the gutter and at the funnel. They need changing and washing pretty often if you are going to be drinking the water and storing it in your main tank, as even small particles will grow bacteria given half a chance. The first is from a pair of thick tights, that stops leaves and insects. Further along I made material filters of densely woven cleaning cloth and then a double layer of muslin in the funnel which shows up any grime and tells you your filters further up the system need changing. It all sounds pretty excessive but any bits will build up at the bottom of your main water tank and grow algae and mould.


On boats, 20litre plastic containers seem to be mostly used which are lightweight and allow you to see the water but aren’t good for keeping it longer than a couple of days as sunlight and daytime temperatures encourage bacteria growth. Just as house people store water underground, we need to keep our drinking water in the coldest, darkest place we can. If you don’t have a main fresh-water holding tank, it’s a good idea to find that cold dark spot on your own boat.

If you do decide to store rainwater in your main tank, it’s worth remembering that even carefully filtered rainwater will have impurities that chlorinated tap-water does not, so I run off any water that has been sitting in there unused for over 3 weeks. I don’t properly know the science behind all this, just going on what I’ve read in books like ‘The Humanure Handbook’ (Jenkins), and various rainwater-harvesting pamphlets.


The moment you decide to add rainwater in your main tank, you are tied into responsibility for your health and of anyone else using your boat. The water coming out of your taps is not ‘pure’ anymore! It’s true that we were drinking water straight from mountain streams for centuries without too many problems but this stuff has rained through a polluted sky, trickled over the bird poo and leaves on your roof and been sitting in your tank for a few days.

I use this water straight out the tap for washing my skin, hair, dishes and clothes and am still alive. But for drinking and cooking with, I purify it. The usual water filters used on boats won’t remove pathogens, just particles.

There are several ways of killing off any nasty bacteria that could make you and especially vulnerable people like children or elderly folk, ill. I guess it’s a case of finding the method that suits you as they all have drawbacks!


If you boil the water between 5 and 10 minutes (just turning it off as it begins to boil is no good apparently), you’ll kill pretty much everything. I don’t use this method because it wastes large amounts of gas, or takes far too long on the wood stove. It creates condensation which as we know, is no friend to the boater. It also needs cooling to use for drinking which means being very organised.

U.V treatment:

A constant supply of electricity is needed to feed this method, equivalent to running a 60W light bulb. You can buy kits that fit under sinks and expose the water to ultra violet light that kills bacteria. I’ve read that it’s very effective if the water is filtered well beforehand and of course there are no chemicals added. My electricity is from solar panels so it wasn’t right for me.


This is what our domestic house water is treated with of course and it’s probably the easiest solution. You can add ‘water purification’ tablets in as directed. It’s worth doing some research on chlorine before deciding on this method.

Ceramic filters:

This is what I use, but again, I’d advise others to research it properly before going for it. The water is absorbed through ceramic filters (called candles) that have had colloidal silver baked into the clay which is a natural antibiotic. It takes a while to filter through so I fill the filter up in the evening and it’s ready by morning. Mine is like a tea-urn with a tap at the bottom and was made in England and cost about £85 (British Berkfeld SS gravity filter). The water tastes really good and clean and I’m happy with this method, although I have worries about the sourcing of silver, even if it is in microscopic quantities. Also, there’s been a recent development of nano-technology in the world of filters which people might want to research before buying.

I’ve only been harvesting rainwater for a few months but it’s already been really useful. I haven’t had to move my boat to find a water point as often and during the stoppages, used solely rainwater for 3 weeks. From 50 square feet of collecting surface, I’ve had about 190 litres a month (over autumn/winter – it’ll be much less in the summer). I think that’s about 7 litres a day but of course it’s not spread evenly throughout the month.

Things I would do differently: I shouldn’t have bought the corrugated sheets. They’re sturdy and clean and it makes a good greenhouse and keeps my wood dry but I feel guilty about all that plastic crap.

By the way, if you are relying entirely on rain for drinking water, you need to re-mineralise it as water from streams and wells passes through sediment and over rocks and gathers all the minerals we need for good health. One person I know who does this, keeps granite and other rocks in the bottom of her filter.


The water flows down towards the front of the boat→

The guttering is in two parts which means you don't need a high starting point to get the water to flow down into the funnel and water tank.

boiling the water is best...

I believe there are lot's of water purification systems.I learned about some methods when I was in grade 8. Rain water is regarded as one of the best form of drinking water if it is naturally purified i.e without adding extra chemicals. Here the process of distillation and purification can also get a good place. For me I always drink boiled water as it is said that if the water is boiled properly it will remove the germs from the water. Though it wastes more amount of gas and other things, I think boiling is one of the best thing for purification. I have not studied about the ceramic filters but I use simple water filters for the purification of water after it is boiled. We can also see many products in the market for purifying water. Are these types of products useful and does it make any side effects?

Drinking Canal Water

I have a system which involves using canal water rather than rain water. On my front deck I have three 25 litres drums linked by pipes. The first is the initial hopper, into which I pour raw canal water. This passes via a pipe to the top of the second container. This one is the filter and is stuffed with PET insulation wool (recycled plastic bottles made into loft insulation). The water passes through the filter and passes via another pipe to the third container which is the sedimentation tank - here any remaining debris can settle to the bottom. Finally the water is taken from the top of this tank by pipe into the main water tank.


This system cleans the water well enough for all uses except drinking and cooking. For this I boil water in small quantities and put it through a British Berkefeld ceramic filter. I end up with beautifully clear and good tasting water.

I also add bleach - the unscented variety of course, which will kill most pathogens. This releases chlorine into the water, which should evaporate by the time you drink it. If the water tastes of swimming pool, you've used too much.

I've been using this system for several months now and no tummy bugs etc. They say your body is 95 per cent water - so mine must be 95 per cent canal water by now!


Boat Gypsy

Water Filtration System

This system sounds like an interesting water filtration system. Does it seem to be working well for you? I'm not sure how I would feel about putting chlorine into the water on my own. I would be afraid that I would put too much in.

canal water

As Boat eluded to, but did not say, the chlorine will evaporate in a few days. So taste the water, if it tastes like chlorine, just let it sit a while longer, maybe even in an open container.


water harvesting & purification

Just getting a rainwater harvesting system in place on my boat - very exciting! For purification, as people will know, you have 3 main choices: Chlorine (which our mains water system uses but which is toxic in higher quantities and has a growing number of detractors), U.V treatment (great, but requires a constant source of power which is problematic on a narrowboat) and then there is the ceramic filter - a filter which has colloidal silver content which destroys bacteria such as E-coli, typhus etc. I hadn't heard about this until I discovered a brilliant website called Potters for Peace (http://www.pottersforpeace.org/).
Searching for something similar in this country, I bought a British Berkfield water purifier , made in the UK and using the same principle (though it looks like a tea-urn at a village fete - very English!).
Actually collecting the rainwater can be a big challenge as most boats have their water tank at the front and the boat slopes down at the back, so water flows in the opposite direction. I hope I've found a solution and will get my system up and running shortly, so I'll post back if it all works!

water filtrtion

we just got a fairey ceramic from bob bagley at fountainfilters.co.uk
it works the same as a seagul which is advrtised in canal world.
you could technically use canal water but it would clog filter up really fast but wll rotect you from the stuff that grows in the tank.
it cost us £125 and a cartridge replacement is about £40 every 2 years for a two person household although if using canal water it wld be every 3 months!
it goes under sink and has its own tap to plumb in and the flow rate is a 3-4 liters a minute . bob bagley is a dear! call him on 01538750387