What Size Marine Watermaker is right for my Boat?

May 12, 2019

Marine watermakers should provide ample fresh water to all passengers onboard on a daily basis. As a guideline, the U.S. Coast Guard recommends that 30 gallons of water per person per day should be available onboard. So, for example, if you are planning to have 4 people onboard, then you should plan on having 120 gallons of water available per day.

Calculating the Amount of Water Needed

When calculating the amount of water you will need don’t forget to consider all the uses.

Salt water can be used for:

  • Taking showers (but you’ll want to rinse with fresh water at least once at the end)
  • Washing dishes
  • Cooking (this depends on what you are cooking)
  • Washing your hands

You’ll use desalinated water for rinsing the decks, cooking, showering, and drinking. Remember to calculate the drinking water you bring in bottles as well as your storage tanks.

For an easy and quick calculation on how much water you need you can use our calculator on our homepage here. (scroll down to the section called “How Much Water Do You Need.”)

How Long to Run the Watermaker

Next, determine how many hours per day you want to operate the watermaker to make the capacity that you need. Most people are comfortable with between two and five hours per day.

Then, compute how many gallons of water you need to make per hour to make your daily demand considering the period of time you would want to operate the watermaker. Considering the example above, if a person wanted to make 120 gallons of water in a two-hour time period, then a watermaker capable of producing 60 gallons of water per hour is required.

This survey report shows some interesting facts about water onboard yachts.

Marine watermakers are rated based upon how many gallons of water they are capable of producing per hour. This information is also stated in terms of daily production (that is, the rated hourly production multiplied by 24).

WaterMaker Output

Marine water makers are typically available in ranges of production from eight to 344 gallons per hour (that is 200 to 8,300 gallons per day). Larger commercial-sized systems are typically available in outputs up to 1,750 gallons per hour (42,000 gallons per day). Unlike competitors, FCIWatermaker units are engineered to deliver the advertised output under varying conditions.