Fresh Water Aboard a Hunter 290

Every cruiser eventually does the same arithmetic. You look at the water tank, you look at how far you want to go, and you start wondering what it would cost to stop worrying about it. Here's what we found when we actually priced it out for our Hunter 290 — the packaged units, the DIY route, the power budget, and the answer we didn't expect.

There is no $1,000 watermaker

Start with the bad news, because it saves a lot of shopping. Nobody sells a packaged 12 volt marine watermaker for under a thousand dollars. Not on sale, not used, not from a discount outfit. The floor for a real marine unit is roughly three and a half grand.

Prices checked August 2026. Note the second row: $3,480 buys you a unit you operate by hand, at about a gallon an hour, until your arm falls off. That's the price of the technology, not the price of the convenience.

So if $1,000 is the number, you're building it. That's fine — this is an open source boating site, building it is the whole point. But you should know going in what you're signing up for.

How a small watermaker actually works

Reverse osmosis is conceptually simple and mechanically demanding. Seawater sits at roughly 35,000 parts per million of dissolved salt, and its osmotic pressure is around 350 psi. To push water backwards through a membrane against that gradient, you need to beat it convincingly — a small marine system runs somewhere around 800 to 900 psi.

That pressure is the expensive part. Everything else in the system is plumbing.

Note the proportions: most of what you pump goes back over the side as brine. On a small system like this you're recovering only around 15 to 20 percent of the feed water as drinking water. That inefficiency isn't a flaw — it's what keeps the membrane from silting up.

The under-$1,000 DIY build

The standard small-boat design in the cruising community is a Pumptec 107SS plunger pump driving a single 2.5 × 14 inch seawater membrane. It's the smallest sensible seawater RO setup, it runs on 12 volts, and the parts are all available off the shelf. One well-documented build of exactly this puts out about 3 gallons per hour at 900 psi while drawing roughly 14 amps.

The used pump is the whole game. Everything else on this list is close to a fixed cost, and the Pumptec is the single biggest line item. They turn up regularly on eBay and through misting and pressure-washer surplus dealers — watch for a few weeks rather than buying in a hurry, and $1,000 is a real number. Buy it new and you're at $1,500.

Build it portable, not installed

This part is specific to boats our size, and it's the single best decision in the whole project. Don't plumb it in.

A Hunter 290 has no spare through-hull and no machinery space worth the name. Cutting a new hole in the hull for a watermaker intake, on a 28-foot boat, to feed a system you'll run a couple of hours a week, is a poor trade. So: mount the whole thing in a milk crate or a plastic toolbox — pump, vessel, prefilters, gauge, valve. Intake is a weighted hose over the side. Output is a hose into the deck fill.

It lives in the cockpit locker. It comes out when you want water. No hull penetration, no permanent real estate lost, and — the part people forget — it goes with you to the next boat, or gets sold for most of what you paid. This is exactly the architecture the commercial portable units use. They just charge five thousand dollars for it.

The power math is the real constraint

Here's where the project actually gets decided, and it isn't money.

The high pressure pump pulls 15 amps. The feed pump adds about 3. Call it 18 amps while running. Two hours of runtime gets you roughly 6 gallons and costs you about 36 amp-hours.

Now look at the other side of the ledger. A stock 290 house bank is likely a couple of Group 27s — call it 100 amp-hours you can actually use without abusing them. So one water session is a third of your usable bank, spent on six gallons.

Which is a nice way of saying the watermaker isn't really a water project. It's a solar project with a plumbing attachment.

And then we asked the obvious question

The Hunter 290 carries 40 gallons. Two people living carefully at sea use about 3 to 4 gallons a day. That's ten to thirteen days of range sitting in the tank already.

We're coastal cruising. We are never more than a few days from a hose.

So the honest conclusion, after all that pricing: we don't need a watermaker. We need maybe four to six gallons a day of top-up, and there are much cheaper ways to get it. Spending $1,000 and 36 amp-hours per session to solve a problem the boat doesn't have is exactly the kind of thing this site exists to talk people out of.

What we're doing instead — the $400 water plan

The foot pump is the headline. It plumbs into the existing galley line in an afternoon, keeps the pressure system intact for when you want it, and two people on a foot pump land around 2 gallons a day. That alone takes 40 gallons from about ten days to about twenty.

Add the jugs and you're at three weeks of independence. Add a rain catcher and you're at "we stopped counting." For coastal work, that's more range than we'll ever use before the next fuel dock — for a third of the price of the DIY watermaker and none of the amp-hours.

Sources

• Sailboatdata — Hunter 290 specifications (40 gal water, 20 gal fuel, Yanmar 18 hp)
• SeaWater Pro — 12V single membrane watermaker ($4,295, 17 GPH, 600 W)
• Defender Marine — Katadyn Survivor 35 ($3,480, 1.2 gal/hr manual)
• Abroad Reach Travel — DIY Watermaker build log (~3 gal/hr at 900 psi, ~14 A, parts list)
• Misting Direct — Pumptec 107SS 12V pump and motor ($629, 0.25 GPM, 15 A at 12 VDC)
• Hydrocomponents — 2.5 × 14 in 1000 psi pressure vessel ($396)
• Hydrocomponents — DIY watermaker guidance (low feed flow and membrane scaling)
• Practical Sailor — Install a Water Saver: A Galley Foot Pump
• Defender Marine — Whale Gusher MK3 galley foot pump
• All At Sea — Harvesting Rainwater on Your Boat

All prices checked August 2026 and will drift. Treat them as a shape, not a quote.