There is a huge amount of water spread out in front of us on the ocean...

In fact, there is not a drop of “drinkable water”.

It is in the world of shipping that we live in such contradictions.

So how do ships that make long voyages and people who live at sea secure water?

Even here on board ships, desalination equipment using seawater desalination technology is installed.

In this issue, we will introduce three typical methods of "creating fresh water from seawater on board”.

◾️Distillation Method ～Making Water with Engine Heat～

The traditional standard method is the distillation method.

The mechanism is simple: seawater is heated to evaporate, and the vapor is cooled to extract only water.

A ship's engine produces a lot of heat while underway. The distillation method efficiently produces water by heating seawater using the heat from the cooling water that prevents the diesel engines from heating up, in other words, waste heat. This method is widely used in large cargo ships, self-defense ships, and other vessels that operate for long periods of time,and 90% of all desalination systems for ships are of this distillation type.

In recent years, however, ship improvements have been made to reduce power output during navigation in response to energy-saving measures aimed at environmental protection and economic improvement. As a result, the amount of cooling water required to heat seawater is decreasing, and the temperature of waste heat tends to drop as well. In response to these problems, technology is being developed every day to continue to produce the necessary amount of water with the exhaust heat, which is becoming more limited every year, such as by vacuuming the inside of desalination equipment to reduce pressure and promote low-temperature evaporation.

👍Advantages

・Very good water quality (close to pure water)・Less affected by salinity of seawater

・Can use “residual heat” from engines to produce water

👎Disadvantages

・Device is large and requires regular maintenance

・It is becoming more difficult to ensure the necessary temperature for heating as engines become more energy efficient

◾️Reverse Osmosis (RO) Method ～Cutting Salt through a Membrane!～

A method that has been attracting attention in recent years is the use of "reverse osmosis (RO) membranes”.

This was also used in the “Mamizu Pia” introduced earlier.

By passing seawater through a “special membrane” under high pressure, only water molecules are extracted and salt and impurities are shut out. Many devices using reverse osmosis membranes are compact and suitable for exploration ships, yachts, and small vessels. They can also be combined with solar power generation, as they run on electricity.

👍Advantages

・Compact and easy to install on ships

・Produces high purity fresh water

👎Disadvantages

・Daily maintenance such as membrane replacement and cleaning is essential

・High pressure pump power required

・Initial cost may be higher than distillation type for installation on large vessels

◾️Solar Still ～Making Water Only with The Power of The Sun～

What if the electricity and engines are not working?

Solar stills (solar distillers) are useful in such cases.

This is a device that slowly evaporates seawater with the heat of the sun and collects the vapor that comes out to convert it into drinkable water. It is installed in emergency lifeboats, etc.,and quietly produces water without using any electricity. However, the amount produced is quite small, so it is only for "emergency" use.

Recently, hybrid methods, such as a combination of evaporation + RO, have been introduced.

Japanese Self-Defense Force destroyers are often equipped with both evaporation and RO.

◾️Will water production technology change the future?

This onboard desalination technology is now being deployed not only at sea, but also for emergency relief during disasters and in regions with limited water resources.

Combined with renewable energy, a future in which they can be used as “self-sustaining water supply units” is just around the corner.

Ocean water becomes drinking water.

This may be one form of human technology interacting with nature.