Fresh water autonomy on a catamaran: tanks, watermaker and good habits on board

On a cruising catamaran, fresh water autonomy rests on three pillars: the capacity of the onboard tanks (300 to 960 litres depending on the Lagoon model), production via watermaker (reverse osmosis, 30 to 250 litres per hour), and consumption discipline on board (20 to 80 litres per person per day depending on the comfort level you aim for). Sailoe has managed its Lagoon fleet in-house in the Seychelles and in Guadeloupe for more than 20 years: the field feedback shared here comes directly from experience, from seasonal recommissioning procedures and from crew briefings before every departure.

How much fresh water should you plan per person per day on board a catamaran?

Consumption varies with the comfort level you aim for: count on 25 litres per person per day for measured offshore sailing, 35 litres for standard cruising, and up to 70 to 80 litres for comfortable charter with cooking on board and regular showers. This starting calculation sizes everything else: the tank, how often the watermaker runs, the load on the batteries.

Usage breaks down into four categories: drinking and cooking (3 to 5 litres), personal hygiene (10 to 15 litres), washing up (5 to 10 litres), various rinses (5 to 15 litres). On a tropical charter - Seychelles or Guadeloupe mode - a crew of 4 people consumes between 140 and 320 litres per day depending on habits. On Sailoe crewed cruises, the crew sizes the systems for 50 to 70 litres per person per day: that is the range that guarantees comfort without waste.

What is the fresh water tank capacity on a Lagoon catamaran?

Lagoon catamarans carry between 300 and 1,000 litres of fresh water depending on the model. On a Lagoon 51, the 830 litres cover roughly 5 to 7 days for a crew of 6 people consuming 25 litres per person per day: it is the safety cushion that precedes use of the watermaker, not the main source on a long cruise.

Fresh water tanks across the Lagoon range: an overview from 300 to 1,000 litres

The table below brings together the capacities verified on the sailing Lagoon models offered for charter. The estimated autonomy figures are calculated on a basis of 50 litres per person per day - that is a crew of 6 people in standard comfort.

Lagoon model	Fresh water capacity	Estimated autonomy (6 people, 50 L/day)
Lagoon 38	300 L	~1 day
Lagoon 42 Millenium	300 L	~1 day
Lagoon 43	300 L	~1 day
Lagoon 46 Iconic	600 L	~2 days
Lagoon 47	700 L	~2.5 days
Lagoon 51 Iconic	830 L	~2.8 days
Lagoon 55	960 L	~3.2 days
Lagoon 60	960 L	~3.2 days
Lagoon Sixty 5	1,000 L	~3.3 days
Lagoon Eighty 2	1,000 L	~3.3 days

On the Lagoon 55, 60 and larger units that Sailoe operates in the Seychelles, the 960-litre tanks make it possible to last 3 to 4 days without production before switching on the watermaker. For long passages, a 30 to 50 litre flexible backup reserve remains good practice.

To discover the full range and choose the model suited to your project, see the Lagoon catamaran range available at Sailoe.

How does a watermaker work on a catamaran?

The watermaker turns seawater into drinking water through reverse osmosis: a high-pressure pump forces salt water through a semi-permeable membrane that retains salt, bacteria and chemical contaminants. The filtered water comes out ready to use at the tap, while the salty concentrate (brine) is discharged back into the sea. The principle is simple, the maintenance less so: that is where reliability on a long cruise is decided.

Flow rates vary with the model installed on board. A compact 12V watermaker produces 30 to 60 litres per hour. A standard model for a 40 to 50 foot catamaran produces 60 to 120 litres per hour. Large units climb to 150 to 250 litres per hour. On the Lagoons equipped by the builder, the compact watermakers range between 60 and 90 litres per hour in economy and full-power modes. Running 2 to 3 hours per day, an installation of 60 to 80 litres per hour comfortably covers a crew of 4 to 6 people in standard comfort.

What is the difference between a 12V watermaker and a 220V watermaker?

A 12V or 24V watermaker runs directly off the boat’s batteries, recharged by the solar panels. The flow rate is more limited (30 to 60 litres per hour) but autonomy is total as long as the sun shines: no generator, no noise, no diesel. It is the ideal configuration in the Seychelles or in Guadeloupe, where solar radiation exceeds 250 days per year. A compact watermaker consumes about 300 Wh for 60 litres produced: with 400 to 600 Wp of solar panels, the watermaker runs for free every day without drawing on the batteries.

A 220V watermaker offers more flow (150 to 250 litres per hour) but requires running the generator or plugging into the marina’s 220V supply. More noise, more constraint, more operating cost. The 2025-2026 trend is moving towards low-consumption reverse osmosis systems with energy recovery from the brine, which halve the electrical consumption compared to conventional installations.

How do you maintain the watermaker to avoid breakdowns at sea?

The watermaker is the critical point of fresh water autonomy: a breakdown mid-passage can turn into a serious situation. Three maintenance steps prevent the vast majority of problems. First, rinsing with fresh water after each use - this step prevents salt from calcifying the membrane during extended stops. Second, checking the sediment filters before each departure. Third, chemical preservation if the boat is laid up for several weeks.

You also need to avoid using the watermaker in a polluted port or in turbid water: membranes fouled by hydrocarbons or suspended matter do not rinse out easily. Regular membrane maintenance, as recommended by the manufacturer, determines the durability of the installation. On the Sailoe fleet, the technical team checks the watermaker at every seasonal recommissioning: it is a non-negotiable procedure that explains why watermaker breakdowns remain rare even in a demanding tropical environment.

What tips help reduce fresh water consumption on board?

Reducing your consumption on board is not a constraint but a habit acquired from the very first days of sailing. A few simple actions can halve consumption without sacrificing comfort. A seawater shower followed by a fresh water rinse goes from 20 to 30 litres down to 3 to 5 litres. Washing up by soaking in seawater with a final fresh water rinse cuts the kitchen’s water use in half.

Other habits are learned quickly: taps with low-pressure aerators (standard equipment on charter fleets), seawater-flush marine heads, rainwater collection through the roof gutter system (very handy in French Polynesia and the Caribbean during the wet season). One telltale sign of a leak in the circuit: the automatic pump kicking in every 10 to 15 minutes with no use in progress. On Sailoe crewed cruises, these habits are explained right from the departure briefing so that the whole crew adopts the same reflexes from day one.

Which fresh water setup should you choose for a long voyage by catamaran?

For a voyage of several weeks in the Seychelles, French Polynesia or the Caribbean, the optimal setup combines a tank of at least 500 to 700 litres, a watermaker producing 60 to 100 litres per hour, and a solar supply sufficient to run it without the engine. The three elements are inseparable: a watermaker without enough solar energy becomes a burden, not an asset.

Sailing profile	Recommended tank	Watermaker	Power supply
Coastal cruising (frequent stops)	300-400 L	Optional	Standard
Two-week cruise (a few stops)	500-700 L	60-80 L/h recommended	200-400 Wp panels
Long offshore voyage (long passages)	700-960 L	80-120 L/h + jerrycan reserve	400-600 Wp + lithium batteries

A 12V watermaker paired with 400 to 600 Wp of solar panels runs in complete autonomy in a tropical zone. On the Lagoons in the Seychelles and in Guadeloupe, all Sailoe boats suited to long cruises are equipped with watermakers checked before every departure by the same technical team present on both bases.

To prepare a long-distance voyage - itineraries, anchorages, logistics - the article long voyage by catamaran details all the steps for preparing an offshore passage.

If you would like to get a taste of long-distance sailing without managing the technical side yourself, Sailoe offers crewed cruises with a full crew in the Seychelles and the Caribbean. The watermaker is managed by the professional crew, meals are prepared on board, and you enjoy the boat’s autonomy without carrying its constraints. For those who prefer to sail independently, the fleet of Lagoon catamarans for charter includes watermaker systems on the units suited to long cruises. To find out more or receive a quote within 24h: charter@sailoe.com / +33 2 97 84 61 61.

Frequently asked questions about fresh water on board a catamaran

What is the average water consumption per person on board a catamaran?

For measured sailing, count on 25 to 35 litres per person per day. On a comfortable charter with cooking on board and regular showers, this consumption rises to 70 to 80 litres. To size your reserves safely, use 50 litres per person per day as your calculation basis. A crew of 4 people over a week therefore needs about 1,400 litres - roughly twice the tank capacity of a Lagoon 51 - so you have to combine the tank with daily watermaker production to cover the week.

Is a watermaker enough to cover all the water needs of a catamaran?

Yes, provided it is correctly sized and supplied with electricity. A watermaker producing 60 to 80 litres per hour, running 2 to 3 hours per day, covers the needs of a crew of 4 to 6 people in standard comfort. Solar power is the key in a tropical zone: with 400 to 600 Wp of panels and sufficient batteries, the watermaker runs without running the engines.

Is it possible to live in complete fresh water autonomy on a catamaran?

Technically yes, thanks to the combination of tanks, watermaker and rainwater collection. Complete autonomy over several weeks is possible on long offshore cruises, provided you have a reliable, well-maintained installation. The only serious unknown remains a watermaker breakdown: that is why it is advisable to always carry a backup reserve of 20 to 30 litres in jerrycans and the critical replacement parts (sediment filters, a spare membrane for a long passage).

Is the water produced by an onboard watermaker drinkable?

Yes. Reverse osmosis removes bacteria, viruses, salts and chemical contaminants. The water produced is drinkable and of a quality comparable to bottled water. Some sailors add a remineralising filter or mineral drops to recover a taste closer to spring water. On recent Lagoon catamarans, the integrated filtration systems also guarantee the elimination of residual micro-organisms in the storage tanks.