🇬🇧 Fresh Water Generator on board – How we produce drinking water in the middle of the sea

Fresh Water Generator in the engine room of a cargo ship that converts seawater into drinking water.

Fresh Water Generator on board – How we produce drinking water in the middle of the sea

Read the article in 🇬🇷Greek Language

When someone has never worked on a ship, they usually think that the water we use for drinking and daily use is stored before the voyage. In reality, however, on most cargo ships, most of the water is produced on board the ship itself.

As an engineer in the engine room, I have seen many times how important this system is. The Fresh Water Generator is one of the most useful machines in the engine room, because it allows us to convert seawater into clean water for use on the ship.

In practice, every time I am on a multi-day voyage, I know that the proper operation of the Fresh Water Generator is crucial for the daily life of the crew and for the operation of the engines.

What is a Fresh Water Generator

A Fresh Water Generator (FWG) is a desalination system used on ships to produce fresh water from seawater.

In the engine room of a cargo ship, this system exploits the heat of the main engine to evaporate seawater and create clean water through condensation.

In my experience as an engineer, the FWG usually operates when:

the ship is sailing normally

the main engine is running

there is sufficient heat from the jacket cooling water

This system allows us to produce several tons of water daily without having to load large quantities from ports.

Why is it so important on board

On board a ship, water is used for many different needs.

In practice, in the engine room I know that fresh water is used for:

drinking water

cooking

showering and daily hygiene

laundry

engine room technical uses

On a large cargo ship, the crew can consume many tons of water per day.

If the Fresh Water Generator is not working properly, then the ship must rely only on the water reserves in the tanks.

I have been in cases where the system has failed and then water management becomes much more careful.

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How the Fresh Water Generator Works

The basic operating principle of the system is relatively simple but extremely effective.

In the engine room, the FWG operates at low pressure (vacuum). This means that the water can evaporate at a temperature much lower than 100°C.

The process has the following stages:

1. Vacuum creation

The system creates a negative pressure inside the evaporator.

This allows the seawater to boil at approximately 40–60°C.

2. Water heating

The seawater is heated by the cooling water of the main engine.

This is very practical because we use heat that would otherwise be lost.

3. Evaporation

The water evaporates and leaves behind the salt and impurities.

4. Condensation

The steam cools and turns back into a liquid.

This liquid is now fresh water without salt.

5. Water collection

The produced water is led to the ship's fresh water tanks.

Water production on board

Depending on the size of the ship and the system, a Fresh Water Generator can produce:

10 tons of water per day

20 tons of water per day

even more on large ships

In my experience, on most bulk carriers the production is around 15–25 tons per day.

This is enough to fully cover the needs of the crew.

Click on the photo for more.

Fresh Water Generator Maintenance

Like all machines in the engine room, the FWG needs proper maintenance.

In practice, as an engineer I often check:

vacuum pressure

temperatures

salinity of the water

condition of the plates

One of the most important elements is the salinometer.

This instrument checks the salinity of the produced water.

If the salinity is high, then the water is automatically discharged and not directed to the tanks.

Common Fresh Water Generator Problems

In my years in the engine room, I have seen the system encounter problems several times.

The most common are:

low vacuum

If there is an air leak, evaporation does not occur properly.

dirty plate surfaces

Salts can reduce the efficiency of the system.

low jacket water temperature

Without enough heat, proper evaporation does not occur.

problems with the ejector

The ejector is responsible for creating vacuum.

If it does not function properly, the system stops.

The Importance of the Fresh Water Generator in the Engine Room

For us engineers, the FWG is one of the systems that works almost every day on a voyage.

I have seen many times how important it is to have it working properly, especially on long voyages where the ship is weeks away from port.

The production of water on board a ship is something that most people never think about, but for the crew it is a key part of life at sea.

Every time I check the system in the engine room, I am reminded of how important its proper operation is for the comfort and safety of the crew.

📌 The video is aimed at:

AEN students

Merchant Marine engineers

Friends of shipping

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Naval engineering is not just power — it is control, knowledge and proper timing.

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