Dehydration on a Boat Sneaks Up Fast

Dehydration is a serious risk on a boat, and it can sneak up fast, even on a mild day when you never once feel thirsty. Out on the water you sit in sun and wind for hours, you are often working hard, and you rarely get a break in air conditioning, so you lose more fluid than you realize.

Staying hydrated on a boat takes a little more thought than it does on land. The drinks we reach for don’t help, either. Coffee in the morning, iced tea in the afternoon, a sundowner at night: caffeine and alcohol are both mild diuretics, so they quietly work against you.

Fresh water isn’t unlimited aboard, so there’s a natural pull to ration it. And honestly, slightly warm tank water just isn’t that appealing.

Add in that the early warning signs are easy to miss, and you have the perfect setup for trouble. The good news is that dehydration on a boat is easy to prevent and easy to treat, once you know what to watch for.

What Raises Your Risk

A few things make dehydration far more likely, and some of them are not well known.

Medications are the big one. A surprising number of common prescriptions make you lose fluid faster. You shouldn’t stop your meds; just be extra mindful about drinking:

• Diuretics, or “water pills” (Lasix is the common one), often prescribed for blood pressure or heart conditions
• Some other blood pressure medications
• Some diabetes medications, especially SGLT2 inhibitors like Jardiance, which flush sugar out through your urine and take water with it
• Medications that cause nausea, vomiting, or diarrhea, which many GLP-1 drugs like Ozempic and Wegovy do
• Laxatives
• Some antibiotics

A few conditions raise the risk too. Diabetes itself matters, because when blood sugar runs high, your body sends the excess out through your urine and pulls water along with it. Seasickness, a stomach bug, diarrhea, or a fever can dehydrate you in a hurry on their own. And pregnancy raises how much water your body needs to begin with, with morning sickness sometimes piling vomiting on top.

Age is the quiet one. As we get older, the thirst signal gets less reliable and the body holds less water to start with, so dehydration arrives faster and with less warning. It’s worth extra attention for anyone aboard who’s past 60.

The Signs Worth Knowing

Caught early, dehydration is easy to treat. The trouble is that the first signs are easy to wave off. A mild case can look like:

• A headache or dry mouth
• Trouble concentrating, or just feeling foggy and short-tempered
• Muscle cramps
• Nausea or dizziness
• Sweating less than the heat seems to call for, or not at all

If it’s hot and you’ve stopped sweating, your body may be too low on fluid to cool itself. That’s a red flag, not a relief. And if you take a drink of water, and immediately break into a sweat, that’s your body telling you it was running low. Drink a lot more.

When it gets more serious, you’ll see fatigue, a faster-than-normal heartbeat, and confusion. Left unchecked, dehydration can lead to heat exhaustion, heat stroke, organ damage, and worse. It is not something to ride out, and if symptoms are severe, you may need to see a medical professional.

A Couple of Easy Checks

You don’t need anything fancy to know where you stand:

• Notice how often you pee. Every couple of hours is a good sign. Much longer than that, and you need to drink more.
• Check the color. Pale yellow is fine. Dark yellow or amber means drink more.
• Try the pinch test. Pinch the skin on the back of your hand. It should settle flat in a second or two. If it stays tented, you’re behind on fluids.

If Someone Is Already Showing Symptoms

If you catch even mild signs, act right away:

• Get them drinking fresh water.
• Replace the salt and electrolytes they’ve lost. We kept rehydration drops aboard for exactly this. They’re sugar-free and diabetic-friendly, which matters if anyone on board is watching their blood sugar. You can buy the Hy-Lyte Electrolyte Concentrate we used at Amazon. Sports drinks, coconut water, or water with a little fruit work too.
• Get them cooler. In rough order of what helps most:
  • If conditions allow and they’re steady enough, getting into the water cools fast
  • Dunk a t-shirt in the water, wring it out, and put it back on, or soak their head and hair
  • Shade, at a minimum
  • A fan blowing right on them, better still if you wet their skin first so the breeze does more
  • Air conditioning is best, but weigh how long it’ll take to get there, since that walk or dinghy ride is probably in the sun
  • If someone is severely affected, very confused, burning up, or not sweating, cool them where they are and get help fast rather than walking them anywhere
• Let them rest. Pushing on while your body and brain are under that kind of stress is how a health scare turns into a real emergency aboard.
• If seasickness started it, anti-nausea medication may break the cycle.

Heading It Off

Better yet, head it off before it starts. None of this is complicated:

• Drink before you’re thirsty. Thirst shows up late, so sip steadily through the day instead of waiting until you feel it.
• Add electrolytes to your water. A few rehydration drops in every bottle, or some coconut water, helps your body hold onto what you drink, especially when you’re sweating hard.
• Go easy on the diuretics. Coffee, tea, and alcohol don’t count toward your water the way you’d hope. I’m not telling anyone to skip their morning coffee. Just don’t let it stand in for water the way we once did.
• Make water easier to drink. A slice of fruit or a flavor packet helps if plain water bores you.
• Eat some of your water. Melons, cucumbers, and oranges are mostly fluid. Watermelon and bananas add back a little potassium (apologies to anyone who won’t allow a banana aboard).
• Stay in the shade. A good cockpit cover earns its keep, and a wide-brimmed hat helps when you’re out in it. Just make sure the hat has a chin strap, or it’ll end up in the drink.

You’ll probably never completely escape the risk of dehydration on a boat. But catch it early, and it’s easy to treat.

How Dehydration Caught Us

I learned all of this the hard way. Dehydration once put my husband Dave in the ER.

We’d gone to Key West in February to celebrate his birthday. It didn’t feel hot, so water was the last thing on our minds. We wandered around town and drank coffee, an iced tea, a beer at dinner, and a shot of rum after. Dave was also on an antibiotic that needed plenty of water, which we sort of forgot about. By the end of the day he hadn’t had a single glass of plain water, and neither of us thought twice about it.

The next morning it hit. Getting from breakfast to the car flattened him. He got worse on the drive back to the boat, shaky and confused, slurring his words, his heart pounding. He thought he was having a heart attack. I took him straight to the nearest ER.

It wasn’t his heart. It was dehydration, bad enough to need IV fluids.

What gets me is that I didn’t recognize it. We’d been cruising for years and had caught mild dehydration before. But the day hadn’t felt hot, we weren’t sweating or thirsty, and dehydration wasn’t even on my radar. Dave was 80 at the time, which didn’t help.

We were lucky there was an ER nearby. In a remote anchorage or on a passage, we would have been on our own. That’s the part that stays with me.

Dave’s bad day wasn’t one slip. It was a stack of things. That’s what makes dehydration on a boat so sneaky. The risk factors pile up quietly. So learn which ones might apply to you, and on the days they stack, drink like it matters before anyone feels thirsty.

A Hand With the Rest of Boat Life

Living aboard means handling the unexpected yourself, often a long way from the nearest help. A scare like Dave’s is one of a hundred small things you sort out as you go. If you’d like a steady companion for that learning curve, The Boat Galley newsletter arrives every Wednesday with a real slice of cruising and liveaboard life, from provisioning and boat systems to the little lessons that make life afloat easier. Come join us.

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