Discover the top 12 smart ways to reduce freshwater consumption on ships. Learn practical strategies, technologies, and case studies that can save costs, improve sustainability, and comply with maritime environmental standards.
Why Reducing Freshwater Usage Matters in Maritime Operations
Freshwater is a precious resource, especially at sea. Unlike fuel or provisions that can be stocked in bulk, freshwater onboard ships is limited, produced at a cost, and sometimes unavailable during long voyages. With increased environmental regulations and growing pressure on global freshwater supplies, reducing consumption has become a key concern for shipowners, engineers, and environmental officers alike.
According to the IMO, freshwater production through shipboard desalination contributes significantly to energy use. A typical crew of 25 may consume up to 7,500–10,000 litres of freshwater daily for domestic and technical use. Reducing this not only saves energy but also decreases fuel consumption and emissions, aligning with the goals of MARPOL Annex VI and the IMO GHG Strategy.
This article explores the 12 most effective strategies to reduce freshwater use on ships—backed by case studies, real-world examples, and up-to-date regulations.
Optimise Watermaker (Freshwater Generator) Efficiency
Most ocean-going vessels rely on evaporators or reverse osmosis (RO) units to produce freshwater. However, many operate at sub-optimal efficiency due to scaling, fouling, or misalignment.
Steps to improve efficiency include:
- Regular descaling of heat exchangers (using Alfa Laval-approved cleaners)
- Monitoring feedwater quality
- Maintaining correct brine discharge pressure
A study by Wärtsilä (2022) shows that optimising RO operations can reduce freshwater energy costs by up to 30%.
Reuse Greywater Where Regulations Permit
Greywater—wastewater from showers, sinks, and laundry—can be treated and reused for non-potable applications such as:
- Toilet flushing
- Deck washing
- Pre-rinsing in the engine room
Modern greywater treatment systems from ACO Marine and BIO-UV meet IMO MEPC.227(64) guidelines and are being installed in many cruise ships and offshore support vessels.
Install Water-Saving Fixtures and Flow Restrictors
A small adjustment in showerheads or tap nozzles can save hundreds of litres per person per week.
Technologies include:
- Low-flow showerheads (<9 L/min)
- Sensor-activated taps
- Push-type faucets to prevent overuse
DNV research shows ships with low-flow fixtures reduced potable water use by 15–20% without affecting crew comfort.
Educate the Crew on Water Usage Habits
Technical solutions mean little if daily habits remain unchanged. Awareness campaigns, briefings, and onboard posters make a difference.
Examples:
- Encourage shorter showers
- Report dripping taps or faulty valves immediately
- Close taps when not in use
One Maersk Line initiative called “Save Every Drop” reduced freshwater consumption across its fleet by over 12% in 2020.
Optimise Laundry Operations
Laundry can account for 20–40% of daily freshwater use onboard. Efficient planning helps minimise cycles and maximise load efficiency.
Suggestions include:
- Use industrial marine washers with programmable load sensors
- Run full loads only
- Consider ozone or chemical-assisted cycles that use less water
Some ships now use closed-loop laundry systems that reclaim rinse water and filter it for reuse.
Use Seawater for Deck and Tank Washing
Whenever possible, seawater should replace freshwater in tasks like:
- Hull and deck washing
- Chain locker cleaning
- Bilge flushing (as per ship and MARPOL guidelines)
Ensure proper separation to prevent contamination of freshwater lines and comply with anti-corrosion precautions. IMO Model Courses stress the importance of separating potable and non-potable lines to avoid backflow issues.
Optimise Boiler Blowdown Practices
Freshwater is also used in boilers for auxiliary steam and heating. Improper blowdown practices waste water and heat.
Best practices include:
- Conducting blowdown at the lowest pressure allowed
- Using automatic TDS controllers to optimise frequency
- Recovering condensate wherever possible
In one case study on a bulk carrier, Alfa Laval’s automatic blowdown control saved 3,500 litres of water and 4% of boiler fuel monthly.
Regularly Check for Leaks in Freshwater Lines
Undetected leaks in pipelines, tank valves, or galleys can lead to thousands of litres wasted over a single voyage.
Routine inspection and pressure testing of:
- Pipe flanges
- Shower and sink fittings
- Hidden pipelines under deck
Digital water meters and flow sensors now allow real-time leak detection.
Minimise Use of Freshwater for Ballast Tank Cleaning
While not common, freshwater is sometimes used to clean ballast tanks or remove residual mud before dry docking. Whenever possible:
- Use seawater or treated greywater
- Plan tank cleaning during port stay when water is more available
This is especially important in regions like Australia and the Persian Gulf where freshwater is scarce and desalination energy-intensive.
Implement Smart Water Monitoring Systems
Real-time monitoring of freshwater tanks, lines, and equipment helps engineers track usage, detect inefficiencies, and improve decision-making.
Features include:
- Tank level sensors
- Flow meters
- Alarm systems for overconsumption
Companies like KROHNE and Emerson Marine offer scalable solutions that integrate into ship automation platforms.
Use Rainwater Harvesting Where Feasible
Some small and medium-sized vessels use rain catchment systems to supplement freshwater supplies. This is particularly effective in tropical areas.
Use Cases:
- Collected water used for deck wash or engine room cleaning
- Helps reduce RO operation and save fuel
While limited in scope, this method supports sustainable maritime practices promoted by the World Ocean Review and Marine Insight.
Schedule and Limit Evaporator Use Based on Load Conditions
Evaporators (used for freshwater generation via distillation) consume large amounts of engine jacket water heat and electrical power. By aligning evaporator use with main engine load, ships can generate water more efficiently.
Operational strategies:
- Run evaporators when waste heat is plentiful
- Avoid use during port stays with low engine loads
Shipowners can integrate this into Energy Efficiency Management Plans (SEEMP) as required under MARPOL Annex VI.
Case Study: Tanker Fleet Reduces Water Usage by 25%
A Middle Eastern shipping company operating 20 crude oil tankers implemented the following:
- Low-flow fixtures
- Crew awareness campaign
- Greywater reuse for toilets and deck wash
After 12 months, the fleet reduced freshwater consumption by 25%, saving around 120,000 litres per month. This also translated into 5% less fuel used for RO units—contributing to their EEDI and CII targets.
Frequently Asked Questions (FAQ)
How much freshwater does a typical ship consume daily? Around 300–400 litres per person per day for domestic and technical uses combined.
Are there any regulations that limit water usage? While there’s no direct cap, water usage affects energy use and therefore CO₂ emissions under IMO’s GHG reduction targets.
Can treated seawater be used for all shipboard purposes? No. Only potable freshwater is used for drinking, cooking, and personal hygiene. Seawater is used for cooling, washing, and ballast.
Is rainwater harvesting practical on large ships? Not usually, but it can be helpful on smaller coastal or passenger vessels in rainy climates.
Do all ships have greywater reuse systems? No. But more newbuilds and retrofits are including them to improve sustainability and meet ESG goals.
Conclusion: A Drop Saved Is a Voyage Earned
Reducing freshwater consumption onboard isn’t just about ticking a sustainability box—it’s about smarter operations, lower fuel bills, and a lighter footprint on our oceans.
Each litre of freshwater saved means less energy used, fewer emissions released, and longer operational autonomy at sea. From greywater reuse to crew training, there’s a solution for every ship type and size.
As IMO regulations tighten and global freshwater stress rises, the maritime industry must take the lead. With new technologies and a change in mindset, ships can sail cleaner and leaner—one drop at a time.
References
- IMO – MARPOL Annex IV & VI
- Wärtsilä Marine – Desalination and Energy Use
- DNV – Energy Efficiency at Sea
- Alfa Laval – Water Management Solutions
- ACO Marine – Greywater Treatment
- Marine Insight – Water Conservation Techniques
- IMO Model Courses – Engineering Operations
- World Ocean Review – Freshwater and the Sea
- KROHNE Marine Flow Systems
- UNCTAD – Review of Maritime Transport