Making Water

The watermaker is running!

Even before we bought Innisfree, one of the things we knew we would want on the boat was a watermaker. Living on a sailboat makes you very conscious of the consumables that support your existence, such as diesel fuel, food, propane, electricity, and of course fresh water. Fresh water is needed for drinking, of course, but also cleaning, laundry, and showers.

Cruising sailors do a lot to manage their fresh water, and it’s not uncommon for people to wash dishes in salt water then rinse with fresh, catch rainwater to fill tanks, re-use grey water, and bathe in the ocean. In British Columbia we’re blessed with good, drinkable fresh water, available for free at just about any dock/marina – with ~400 liters of water tankage on Innisfree, we can easily go for several weeks without refilling, more if we’re careful with our usage. But around the world that’s not always the case – good fresh water can be hard to come by, resulting in many dinghy trips with jerry cans to fetch the water, followed by lots of filtering and treatment while filling the tanks. It’s the well-known irony of the ocean… “water, water everywhere, but not a drop to drink”. If you can make your own fresh water on board, you can always be confident in your water supply and you save the hassle of having to chase fresh water in places where it’s less accessible.

Small watermakers are a relatively recent addition to many cruising sailboats. What’s a “watermaker”? It’s a small desalination system, i.e. it turns salt water into fresh water. Watermakers come in a variety of designs and capabilities, but the fundamental components are always the same, and they’re pretty basic: a high pressure pump, and a membrane (think filter). The high pressure pump pushes sea water onto a reverse osmosis membrane which allows fresh water to pass through, leaving the salt behind. The residual (slightly saltier) brine gets discharged back overboard. The pumps come in a variety of designs largely depending on how the high pressure pump is powered (AC, DC, or engine driven on a belt), and the watermakers deliver higher or lower output depending on the size of the system and its energy consumption. There are basic setups and expensive ones, fully automated and packaged designs, but the principle is simple enough: the least expensive route is to build your own, buying the membrane and using a pressure washer pump or something similar similar. The fancier, high efficiency, automated and packaged systems for a boat like ours can run up to $20k US (nice, if you can afford it). In our case we didn’t go for the high end or the full DIY route, but instead opted for a watermaker that comes more in a kit form… all the pieces are there, but some assembly required. Not only does that save us a lot of money, it also means that we can position the different pieces in the boat where they fit, and storage space is always at a premium on a 36’ boat.

Our Echotec watermaker control panel

Ours is the Echotec 260-DML ( Made in Trinidad, these watermakers have a good history and reputation among cruisers and feature simple components with an emphasis on reliability and maintainability. They are not the most efficient, quiet, or compact designs, but the reliability and flexibility are big deal in my book, and they’re a big step up in those categories compared to a DIY system while also being a lot more affordable than high end systems. Your fresh water supply is not a place for flaky gear.

The reverse osmosis membrane is a 4 foot long tube. It’s is a bit awkward to fit on a sailboat, but we found a good spot in the bow immediately under the anchor locker. Not the easiest access, but it’s nicely tucked away. The high pressure pump uses 38 amps off of our 12V electrical system, and I had run 4 awg cables forward from the batteries when we had the floor apart in the boat yard in anticipation of the watermaker install. There’s more to the system than the pump and membrane, though. Salt water is pulled in from the ocean through a strainer (to keep big things like seaweed out of the pumps), through a boost pump and then through two pre-filters, one that filters particles greater than 20 microns, the second 5 microns. These keep dirt and biological contamination out of the membrane, which is quite sensitive. A control panel features a valve and gauges that allow us to control the pressure in the membrane and achieve the desired flow rate of fresh water out of the system. It also allows us to direct the output into a test hose (and into a bucket). The product water from the membrane is quite soft, so it is passed through a hardener/PH balancer before going into one of our two tanks (we can select which tank).

Left to right: 1. Hardener/PH buffer for product water
2. Carbon filter for removing chorine from tank water when flushing the system
3,4. 20 micron and 5 micron pre-filters for sea water before entering the reverse osmosis membrane
(okay, some of those filter holders are empty… the photo was taken while I was installing)

Finally, before we shut it down, we pull water out of our tanks to flush the system for a minute or two with fresh water, which helps keep the membrane healthy. The fresh water first passes through a carbon filter to remove any chlorine before it goes to flush the system – chlorine is another thing which could be bad for the membrane and can be present in water that we get from the dock.

All in all, it’s a fair amount of plumbing, and it has taken a while to get it all installed. I finally finished on Monday morning (August 16th) and we fired it up for a test while nervously checking everywhere for leaks: a few drips, but nothing major (thankfully!). On Tuesday we gave it the first big test, running the watermaker for three hours and filling up one of our water tanks. So far, so good.

Fresh water from sea water (into the test bucket)

Running the watermaker got me thinking again about energy and water, since really what we’re doing is trading one consumable (energy) for another (water). Much ink has been spilled about the energy-water nexus in the world and coming from a cleantech background it was interesting for me to see it distilled (pun intended) down to reality in our floating home. Tuesday was a moderately sunny day, so our solar panels kept up with the ~400W draw from the watermaker as we produced about 130 liters of water. Keeping numbers round, call that 10 Wh to produce each liter of fresh water. On the boat, careful use could stretch that 130 liters water for a couple of weeks (~10 liters per day), but so long as we have some days with good sunshine it will be easy to replenish – that means longer, more frequent showers, more water for cleaning or laundry, etc. But let’s be honest, even if we take advantage of the watermaker to triple our use to 30 liters per day, we’re still being pretty miserly. The average North American uses ~300 (yikes!!) liters of fresh water per day. 1

I like that with the watermaker a) I’m confident in our water quality, and b) we have one less consumable to worry about – it’s easier to be self-sufficient. With enough sunshine (or diesel, since we can also charge our batteries from the engine inverter), we have all the fresh water we need.

We’re also testing if we can get away from using propane by using electric cooking (an induction cooktop). If we could pull the propane out of the boat our consumables would be down to food and diesel, but we have to see if our electrical systems will keep up with all the demands as the weather turns grey and the days get shorter. With enough wind and sunshine, we won’t even need the diesel very often… wouldn’t that be amazing! Stay tuned.