How do Ships get Fresh Water?
Updated: May 16
Water is essential for human survival, and this holds true even on the high seas. Whether it's for drinking, bathing, cooking, or powering the ship's engines, water is a precious commodity that must be carefully managed onboard marine vessels.
On average, each crew member uses about 70 litres of water per day.
In addition to this, clean, fresh water on a ship is required for the boiler steam plants and engine cooling system. For a ship with 20 crew members, the daily water consumption can range from 15 to 20 tonnes.
In the past, ships relied on stocking up on water supplies before embarking on long voyages, but this posed logistical challenges and limited the ship's range due to the additional weight. Moreover, there was always the risk of metallic or plastic leaks into the water after prolonged hours of storage, making it unsafe for consumption.
Today, modern ships are equipped with high-tech water treatment systems that allow them to produce fresh water while at sea.
In this article, we'll explore how the different water production systems work to keep ships afloat and their crews hydrated.
What is the difference between an RO Watermaker and an Evaporation-based Freshwater Generator?
Evaporation-based freshwater generators and RO watermakers both produce fresh water from seawater, but they differ in the process and technology used to achieve this goal. Here are some of the points of difference:
The technology used: RO watermakers use reverse osmosis as the primary mode of technology, while freshwater generators use vacuum distillation.
Temperature: RO watermakers function at cool temperatures between 25 and 38 degrees Celcius. Fresh water generators, on the other hand, work at a temperature of 55-90 degrees Celsius.
Weight and Footprint: When considering a 25 Ton system for both, we find that the water maker is considerably lighter at 400kg, while the generator weighs 833kg. The Evaporation based Fresh Water Generator is longer and wider than the RO water maker, but slightly shorter than the RO watermaker.
Operates on: RO Watermakers operate on power, while the latter runs on waste heat and power. Hence RO Watermakers are often preferred in larger vessels
Quality of Water (TDS (total dissolved solids)) : TDS of water produced by an RO watermaker is (50-500ppm). In contrast, the water quality from the evaporation based generator is distilled (10 ppm or lower). It can even go as low as less than 2 ppm.
Quality compatibility: Water produced by RO Watermakers can be safely used for potable applications. Water produced by Evaporation based Fresh Water Generators (at less than 10 ppm) cannot be used for drinking due to its lack of minerals and nutrients. This water is typically used for the Engine boiler. If used for drinking, it needs to go through a process of remineralisation.
Spares: You can find parts for RO watermakers easily as they can be interchangeably used and replaced with other brands. Spares for the fresh water generator must be sourced from the original supplier, which often means longer delivery timelines.
Suitable for: Finally, RO watermakers are preferable for voyages and anchorages while evaporation based freshwater generators are more suitable for voyages.
We hope you found our guide to freshwater generators and RO watermakers helpful. If you have a large water purification requirement, you would probably be better off with an RO watermaker.
Improvements in technology have made RO far more energy efficient, making it a preferred choice of most seafarers and offshore oil and gas professionals.
Want to find out more?
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