You Need This Much Water on a Boat (Per Person Per Day)

This article will give you a detailed overview of how much water you need per day while sailing. After all, when it comes to successful life on board, preparation is the key.

How much water do you need on a boat per person? For day trips and races, you need between 1.3 - 6.5 gallons (or 5 - 25 liters) per person per day. For cruising, you need about 20 gallons (or 75 liters) per person per day.

So let's look at these numbers in more detail so that you know exactly how much water you will need.

How Much Water Do You Need Exactly?

Your water needs will differ for each type of sailing. Here's how much you need in different circumstances:

  • In extreme conditions, such as races, you can do with 1.3 gallons (about 5 liters) per day per person.
  • In cases where you need to save water but you want to stay quite comfortable, 6.5 gallons (or about 25 liters) per day per person is enough.
  • If comfort is primary, say you are on a cruising holiday, you will need around 20 gallons (ca. 75 liters) per day per person.
  • And if you don't care about water consumption but rather want to lead the lifestyle you would as if you were on shore, you will use around 40 gallons (or 150 liters) per day.

Things You'll Need Water For

  • Drinking: 0.5 - 0.9 gallons (or 2 - 3.5 liters) per day
  • Showers - 0 - 17 gallons (65 liters) per day
  • Laundry - 0 - 40 gallons (150 liters) per load
  • Cooking - 0 - 1.8 gallons (7 liters) per day
  • Interior/exterior cleaning - 0 - 26 gallons (100 liters)
  • Backup - 0 - infinity

Sincere apologies to those who wanted a straight, single number answer. But that's just not possible when estimating water consumption on a boat. There are simply too many variables. So to make this info more useful and tangible, let's decipher what lies behind these numbers so that in a few minutes you will be able to determine precisely what to prepare for your sail.

Down below I'll explain each of the different water needs in detail.

Drinking: 0.5 - 0.9 gallons (2 - 3.5 liters) per day

That's the non negotiable one. You can save water in many ways, but not this one. You want to stick with the recommendation that women should drink cca 0.5 gallons (2l) and men cca 0.66 gallons (2.5l) of water per day.

Up that by some 15-20 percent if you are in a hot environment (anywhere, as long as it is above 82 Fahrenheit or 28 Celsius) and another 15-20 percent if you are physically active during the day. Which you probably are, after all, it is sailing we are talking about.

Showers: 0 - 17 gallons (65 liters) per day

Oh, showers. The topic of many polarizing discussions on any boat I have been on so far. Why? Well, sweet water showers aren't strictly speaking necessary, making the least amount of necessary water a nice, rounded zero. Salt water washes you just as well (though your shampoo will foam a bit less, which is a bummer). But many people don't like the feeling of dry salt on their skin and hair. If left salty, these individual's morale will drop. And you don't want that on a boat.

Whichever way you lean, if you do stick with salt water showers, remember to moisturize after. Sea salt is healthy, but it does dry your skin up.

So how much? They say an average American needs around 17 gallons (65 liters) for a shower. I don't recommend keeping up with that number unless you are on a megayacht where water conservation isn't really a thing.

On the other side of the specter, a quick, one minute shower will cost you around 2 gallons (7.5 liters) And if you wash with seawater and then use freshwater only to rinse after, you can comfortably do with 1.3 gallons (5 liters) per shower.

Laundry: 0 - 40 gallons (150 liters) per load

Another polarizing topic. The case here is similar to showers. Salt water does just as good of a job of washing your clothes. It weakens the fabric overtime, so you can always wash with salt water and rinse with sweet water.

Laundry machines aren't common on regular boats, but if you have one, expect it to use anywhere from 4 to 40 gallons (15 to 150 liters) per load. If that sounds like a lot, know that washing in hand is not a solution as it tends to consume more water than a washing machine.

It is tricky to estimate a per day consumption here. The numbers are per load, so the per day figure depends on how many people are on board for how many days and how much fresh clothes have you guys packed.

Cooking: 0 - 1.8 gallons (7 liters) per day

Not to keep avoiding a direct answer, but I simply must. Let me attempt to justify the ambiguity.

If you cook with salt water and wash the dishes with it too, your consumption equals to zero. And no, you can't really taste the salt traces in your morning tea. I've tried.

But if you want to use fresh water and cook pasta or something similarly water-dependent and then wash the dishes in fresh water, you are realistically looking at a consumption up to some 1.8 gallons (7 liters) per day.

Interior/exterior cleaning: 0 - 26 gallons (100 liters)

I know, I know, not much of a concrete answer again. But as before, this really depends. Most sailors are comfortable maintaining the cleanliness of their boat using seawater. After all, a washdown with a water hose pumping sweet water can easily cost you tens of gallons.

Let's get practical - salt water boats are made to withstand salt water. That being said, especially the interior wood could use sweet water wipe down every now and then. But you don't need to do this every day, so you don't need to worry about things until you get to a marina with a fresh water outlet.

Backup: 0 - infinity

You never know. It is a good habit to keep a few liters of fresh water in case bad things happen. Maybe your electronics got drenched by sea water and you want to try to salvage it by giving them a fresh water bath (with batteries disconnected, this might work at times).

Or maybe your mooring lines have snapped and the wind has carried your half damaged boat to the middle of the pacific ocean and now you have to live indefinitely on the open water without knowing when will the help come. You know, the usual stuff.

In all honesty, most of the time you won't need your backup water, especially if you are cruising in coastal waters. But when you do need it, the consequences of not having it might range from slight discomfort to fatality. The rule of thumb is to bring 20% extra on top of your total.

In Total

So, all in all, we are looking at some 0.5 - 20 gallons (2 - 75 liters) per person per day. By now you probably understand why the estimation spread is so large and why even that estimate is not necessarily true.

But you also understand what variables come into play and depending on your requirements and lifestyle, you can safely estimate how much water you will need. Multiply that by the number of people and days, add a few percent on top as a backup and make sure you either meet that number in your boat's water tank capacity, or you have a sure way to resupply.

Sweet Water Sources

Now that we've done the math, let's briefly go over where you will get your daily water from.

Your main source of sweet water will be your boat's fresh water tank. A 36-foot cruiser will have around 80 gallons (300 liters) water tank capacity. A 70-foot cruiser's tank will be around 260 gallons (1000 liters).

Aside from that, it pays off to have some bottled water with you. Some people don't trust the cleanliness of water tanks (especially when it comes to charters) and besides, it is a good idea to store your drinking water sources separately.

If you are on holiday, cruising along the Mediterranean coasts, a marina will be within a few hours of sailing most of the time. But unless you find yourself in such a location, make sure you know where you can resupply if needed.

Watermakers are a whole another chapter that deserves an article of its own. Watermaker solutions exist for boats of all sizes, but they cost money to acquire and energy to run. Their output ranges from single to quadruple digits in terms of gallons per hour, depending on their size. If you are planning a long journey without fresh water sources, such as an ocean crossing, and you want to be on the safe side, research your options and consider getting one.

Can you desalinate salt water by yourself? Yes. But you don't want to rely on this. It is possible by collecting evaporated salt water, which can be done with household items. But this is a process so slow and so reliant on weather and conditions that it is likely a slow road to death by dehydration. Recall J. C.. Chandor's nerve wracking film All Is Lost (I know, I know, it's just a film, but they got this right).
Can you rely on rain water while on sea? Again, yes, again, this approach will likely kill you unless you are very lucky with where you are at. I know this probably sounds obvious. But it only serves to remind that aside from what you yourself bring, water is hard to find.

So as with all things sailing, prepare and plan well. Fair winds to you all!

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