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Water, water everywhere—leaving spots on glass, stainless and brightwork. Here’s how to fight back.


Here’s another seemingly simple chore that’s actually a pain—washing down your boat. To get the proper look that modern skippers want, it’s necessary to dry the boat with a chamois or microfiber towel after a full washdown. If you let the water dry naturally in the sun, it often leaves crusty spots of dried minerals that can be a trial to remove. It’s all the fault of hard water, the kind of fresh water most folks get from the tap. If you live in an area with soft water, rejoice— you might not have to dry your boat to keep it spot-free. But then again, you might.

Water that carries high concentrations of minerals is classified as “hard” water, while “soft” water, conversely, is mostly mineral-free. Whether water is hard or soft depends on where it came from. Water exposed to limestone or chalk en route to your faucet will be harder than rainwater—until the rainwater seeps into the earth to become groundwater, where it picks up minerals. Most fresh water has some degree of hardness; if you want soft water, catch rain in a cistern, or melt snow, or pump it from a clear alpine spring. Otherwise, it’s probably hard water.

When hard water dries, minerals stay behind, primarily as spots of calcium carbonate—aka lime. Calcium carbonate is what stalactites and stalagmites are made of, and in essentially the same way, come from evaporating mineral-rich water. The stuff will last for millions of years in a cave, so you can imagine how tenacious it is when it gloms onto a receptive surface, like gelcoat, varnish, metal or glass. You’ve got to get it off while it’s still wet, or keep it off in the first place.

Hard water isn’t necessarily bad. It will leave deposits around shower heads and inside pipes and water heaters that can impede their function, but some health studies indicate that drinking hard water is beneficial, thanks to its minerals. But, as always, some experts disagree. You can buy inexpensive test kits to check your water’s hardness.

Water softeners remove calcium and magnesium, but that doesn’t mean water that’s been softened is completely free of minerals. In most water softeners, the calcium and magnesium in the hard water is replaced by sodium. Sodium is easier on plumbing than the minerals in hard water, but still leaves spots when the water dries. They’re easier to remove than hard-water spots, but you still have to deal with them.

Even rainwater can pick up pollutants on the way down, so letting Mother Nature rinse your boat isn’t always the answer either. Accept it— If you want a gleaming boat, you’ll either have to become familiar with microfiber towels, or create your own source of pure fresh water. Option number one is simpler and cheaper, at least if you’re using your own elbow grease.

Remove the rinse water before it dries and you won’t get water spots. It makes washdown more of a chore, but not as much of a chore as eliminating specks of tenacious minerals. Commit to drying-off after rinsing and you can skip the next few paragraphs; your water-spot problems are solved. Congratulations—you can wash my boat any day.

Maybe you’re like most folks (like me, anyway) whodon’t always take the time to chamois off the rinse water, so now you have water spots. Not only are the spots unsightly, and mark you as a sloppy skipper, but over time the calcium deposits can damage paint, gelcoat, varnish and especially, clear vinyl panels such as Strataglass, or isinglass found in canvas enclosures. These panels are delicate and water spots will scratch them like sandpaper if you roll the curtains up. Best not to let the spots form in the first place, so even if you let the rinse water dry on the rest of the boat, at least wipe down the vinyl.

Almost every manufacturer of boat cleaning supplies makes a water spot remover—but they’re expensive, so start off gently. Try soaking the spots with soap and water to soften them—you might get lucky. If/when that doesn’t work, use white vinegar mixed 50/50 with water. The acidic vinegar breaks down the alkaline calcium carbonate so you can wash it away. Clean a small area at a time and add more vinegar if necessary. Rinse thoroughly and wipe dry. If you’re cleaning spots off gelcoat, you’ll have to re-wax, too. This is the least aggressive approach, and the least expensive: Vinegar costs very little, and you can use what’s left over on your salad.


If the vinegar doesn’t do it, the next step is to use a water spot remover and there are dozens of them on the market. These products attack the water spots, chemically dissolving the minerals so you can wash them away more forcefully than vinegar. Choose one that matches the material you’re cleaning—don’t use glass cleaners on acrylic or polycarbonate, for example. Read and follow the directions. Clean a small, unobtrusive area first, just in case the remover doesn’t agree with the surface.

Be gentle when cleaning water spots off clear vinyl—it takes very little to scratch vinyl, and lime is abrasive. First rinse with fresh water, then wash with a non-abrasive sponge or towel and gentle soap—IMAR Yacht Soap is one, but there are more on the shelves of any chandlery(Strataglass recommends IMAR products to clean and protect their vinyl). Then rinse again and dry the panels with a clean microfiber towel, like you should have done in the first place. In fact, you should probably invest in a pile of microfiber towels, and wash them after every use. Leave the panels unrolled as much as possible, even if they’re clean. Dirt and grime are Kryptonite for clear vinyl panels, so keep your vinyl clean and it’ll last longer and let you see better. Sometimes you can renew scratched and hazed vinyl with a vinyl restorer like Aurora Clear View or similar.

Many boats have large hullside windows, and they have to be wiped dry if you want to keep enjoying the vistas from your stateroom. Unless you have arms long enough to reach the whole window and are agile enough to hang over the gunwale and do the dry-wipe trick without sliding into the sea, you may need to launch the dinghy—or move to a marina with finger docks on both sides of the slip. What a pain; maybe it’s time to hire a boat-cleaning crew with a work float. Or solve the problem by purchasing a water softener that doesn’t add salt. It costs money, but will save you a lot of time, effort and aggravation.

Pure water won’t leave spots, and the best way to get pure water is by reverse osmosis. An effective, but complicated, system connects the onboard watermaker to a second reverse-osmosis appliance designed to purify fresh water. The output goes into the vessel’s tanks, and from there is used to washdown and rinse. Twice-osmosed ­water is very clean: Dometic’s Spot Zero, for example, removes all but a trace of dissolved minerals and contaminants, according to the manufacturer.

Dockside, you can run fresh water directly through the Spot Zero, bypassing the watermaker—but a substantial percentage of reject water goes overboard. If you’re paying for fresh water, or have serious environmental ethics about wasting natural resources, you’re better off desalinating seawater, since any reject water goes back from whence it came.


A simpler answer is to run dockside fresh water through a conventional watermaker—fussy skippers have been doing this for years. The watermaker will produce water clean enough to dry without spots. The modification is fairly simple: Plumb a dockside water inlet to the watermaker boost pump, install a charcoal-block filter in the line to remove chlorine, and a three-way valve at the pump. The valve lets you switch between usual watermaker function, i.e., desalinating seawater, and osmosing dockside water. The watermaker works normally in either case; the difference is only in the water source. There’s still the reject-water issue, though. The upside is, the watermaker gets more exercise, which helps it work better and last longer.

No watermaker? No problem. Dometic builds a portable Spot Zero system. The unit is 4.5 feet long and weighs 150 pounds, so it’s not that portable—but it has wheels so you can roll it like a hand truck. It filters dockside water using the same reverse-osmosis process and produces enough pressure and volume to wash the boat directly from the Spot Zero device. Dometic says the reject percentage is just 20 percent. Fill the boat’s freshwater tanks from the Spot Zero, and you’ll have a clean water supply for washdown when away from the dock, handy for rinsing off salt spray before it can dry and leave spots. You’ll get rid of calcium accumulations on faucets and shower heads, and you’ll have good-tasting water to drink, too.

But you can’t please everyone: Some folks prefer drinking hard water and find ultra-pure H2O tasteless. You’ll have to try it for yourself, perhaps while you’re waiting for your boat to dry spot-free. Maybe it’s the next best thing to the pure Alpine spring.

This article originally appeared in the August 2022 issue of Power & Motoryacht magazine.