Risks of Long Term Use of Desalinated Water
- Rachel Smith
- Mar 25
- 5 min read
In 2025, one of our STCW students asked a question about the risks and side effects of drinking desalinated water over long periods of time. The question arose as he and his crew had noticed physiological changes during longer ocean transits, when they were mostly drinking water produced by the onboard desalinator or watermaker.
It was reported that the crew noticed significant changes to nail and hair condition during a Pacific crossing, and some other transits longer than just a few days. Of course this is anecdotal evidence, and medicine relies on science and evidence based practice, but we were fascinated by these observations and this was enough for us to investigate further.
All of our team have existed on desalinated water at times, but didn’t really notice much difference even over prolonged periods of several weeks at a time. However our research showed that the risks are mentioned by some leading organisations, because desalinators provide safe drinking water to some large land based populations, as well as seafarers.
Safe and clean drinking-water is an essential element of health security and underpins sustainable socio-economic development. But in many parts of the world there is a need to develop and manage alternative sources of safe drinking-water, using the same or similar desalination technology as we see on ocean going vessels. Desalination on land has been gaining a foothold in the water-scarce Eastern Mediterranean, coastal areas of Australia, the USAs West Coast and many small islands including Singapore and the Maldives.
At sea, most vessels carry ‘watermakers’ that use a reverse osmosis system, where saltwater is pushed through tiny pores in membranes under high pressure. This leaves the salt, impurities and bacteria behind. It’s a popular choice due to efficiency and reliability. Onboard systems can produce anything up to hundreds or thousands of litres per hour to meet the demands for drinking water for crew and guests, to fill hot tubs/jacuzzi’s, for the deck team, and laundry.
Water produced by modern watermakers looks as clear as crystal and tastes like expensive bottled water - a long way from its salty, ocean water beginnings. But, we also need to think about ‘healthy’ water in terms of electrolyte balance being just as important as drinking ‘pure’ water.
The growing use of desalination (demineralisation) technologies in drinking water treatment, often results in drinking water with very low concentrations of sodium, potassium, magnesium and calcium, leading to electrolyte abnormalities. Desalination removes salts and minerals, leaving behind very pure but mineral-deficient water. Low-mineral water can affect cell volume regulation and mineral homeostasis in the body.
Consequently, guidance has been developed to ensure the safety of water produced using desalination technology and this revolves around the key chemical and microbial risks associated with the desalination process.
Drinking desalinated water has been deemed safe for the short-term, but is generally not recommended for long-term, indefinite use unless it has been properly remineralised. The safety concern stems from the lack of essential minerals, not the water purification process itself.
So what are the risks associated with long term use?
Mineral Deficiency: Natural water sources provide essential minerals like calcium and magnesium, which the body relies on for bone strength, heart health, and energy supply. Desalinated water is very low in these elements as the process removes essential minerals, leaving water that's ‘hungry’ for minerals, potentially drawing them from your body.
Mineral Leaching: Unmineralised water can cause the body to excrete more minerals than usual, leading to an overall imbalance or deficiency, which cannot always be easily compensated for by diet alone.
Electrolyte Imbalance: Low mineral content can lead to low levels of sodium (hyponatremia), potassium (hypokalemia), calcium (hypocalcemia), and magnesium (hypomagnesemia).
Cardiovascular Disease: Studies suggest a link between consuming desalinated water and a higher risk of cardiovascular disease, ischemic heart disease and high blood pressure.
Iodine Deficiency: The process can strip iodine, increasing the risk of iodine-deficiency disorders, impacting thyroid function.
Kidneys: Ingesting demineralised water can affect kidney function and cause morphological changes, according to some animal studies.
Oxidative Stress: Long-term consumption might induce oxidative stress in the body, affecting cellular health.
Potential Health Issues: Some studies suggest a correlation between long-term consumption and possibly some types of cancer, though more research is needed.
Of course, symptoms of many of these conditions can take months or years to manifest and it’s important to remember that acute symptoms occurring within hours or days are rare. In fact, the symptoms reported by our student related to hair and nails becoming brittle and weak and could easily have been associated with dietary and other factors.
Typical symptoms of a mineral deficiency include:
Headache
Fatigue, weakness, low energy
Confusion, anxiety
Confusion or irritability
Loss of balance
Muscle cramps or spasms
Muscle weakness or paralysis
In severe cases: Seizures, stupor, or coma
Loss of appetite, nausea, or vomiting
Muscle stiffness, twitches, or cram
Shortness of breath
Chest pain
Irregular heart rhythms, palpitations
Seizures
Noticeable symptoms would most likely be associated with other underlying factors, such as poor diet, diarrhoea and vomiting, excessive sweating, exertion/intense activity without electrolyte replacement, alcohol intake, rapid overhydration and some medications and chronic health conditions. So a thorough history and assessment of the patient is vital.
What should you do if you suspect symptoms and how can you treat a mineral or electrolyte imbalance onboard?
First, take a full patient history and carry out an examination to rule out other conditions.
Speak to your telemedicine provider for advice and a treatment plan.
Medical Treatment: For severe deficiencies, a doctor may recommend medical treatments, such as intravenous (IV) fluids and minerals to restore levels rapidly in a hospital setting.
Address Underlying Causes: If the imbalance is due to an underlying condition (e.g., an eating disorder, substance use disorder, or kidney disease), that condition must be managed to ensure long-term balance.
Dietary Modifications: For most minor deficiencies, the primary solution is to incorporate more mineral-rich, whole foods into your diet. A registered dietitian can help create a tailored eating plan.
Supplements: In cases where diet alone is insufficient, your doctor or dietitian may recommend specific mineral or multivitamin supplements at a specific dosage. It's vital to follow their instructions, as excessive intake of some minerals can be harmful.
Lifestyle Changes: Managing stress, ensuring sufficient sleep, and getting regular physical activity can support overall mineral balance and well-being. Proper hydration is also essential, especially after heavy sweating, vomiting, or diarrhea and rehydration drinks can be considered to help maintain mineral levels.
Key Mineral Sources
The best way to obtain minerals is through a varied, balanced diet rich in whole, unprocessed foods.
Leafy greens (spinach, kale, chard, beet greens), legumes (beans, lentils), nuts/seeds (pumpkin, sunflower, almonds, chia, cashews), potatoes/sweet potatoes, squash, avocado, fish (salmon, cod, halibut, tuna), tomato’s, brown rice, bananas, dried apricots, oranges, watermelon, dark chocolate and dairy are great sources of magnesium, calcium and/or potassium.
We can rely on naturally salty foods like pickles, salted nuts, or cheese for sodium, as most people get enough sodium from the processed foods in our diet.
It’s worth checking your itinerary to see if you’re likely to have any longer voyages where the crew might need to rely on desalinated water. If so, think about a plan to keep everyone healthy. This could be as simple as making a selection of rehydration drinks available and ensuring that mineral-rich foods are on the menu.
While most issues come with long term use of desalinated drinking water, it’s sensible to encourage good practice and keep your crew hydrated and healthy.
We hope you’ve enjoyed this blog and picked up a few pointers. Please let us know if there are any topics you would like to see in the future.
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