A marine reverse osmosis watermaker turns raw seawater into drinking water aboard your boat, so you carry less, stop less, and stay out longer. This guide covers how RO works in a marine context, what specs actually matter, how to size the right unit, and which system suits different boats and crews.
How Reverse Osmosis Works in a Marine Watermaker
Reverse osmosis forces seawater through a semi-permeable membrane under high pressure. The membrane passes fresh water molecules and rejects dissolved salts, pushing the brine overboard as waste. A good marine RO membrane rejects around 99.4% of dissolved salts, producing output well under 800 ppm TDS, typically 250 to 300 ppm. That comfortably meets Australian drinking-water standards.
In practice, a marine system has three stages working together:
- Pre-filtration: a sediment cartridge (commonly 5 micron) catches particles before they reach the membrane and shortens its life.
- High-pressure pump: pushes pre-filtered seawater to operating pressure, typically around 800 PSI for seawater membranes.
- UV sterilisation: a UV stage after the membrane provides an additional layer of treatment before the water reaches your tank.
All LEDI watermakers use this three-stage process. The LEDI Scout includes a built-in UV unit and a Pumptec 107SS stainless high-pressure pump rated at around 800 PSI.
Why 12V Matters for Marine Use
Most boats already run a 12V DC house bank. A 12V marine watermaker draws directly from that bank, no generator, no inverter, no separate power circuit. The Scout draws 16 to 18 amps, which a 200 to 400W solar setup handles comfortably while at anchor or underway.
That matters in practical terms: you can make water while sailing in light winds, while anchored off a remote island, or while waiting out weather in a bay with no marina facilities. You are not burning diesel or running a generator to stay hydrated.
If your daily water demand is higher, say for a larger crew, showers underway, or longer passages, the LEDI Nomad runs on 12V or 24V DC, producing 40, 60, or 80 litres per hour to match bigger needs.
Matching Output to Your Actual Needs
Output rating is the most misunderstood spec when choosing a reverse osmosis watermaker for marine use. The number on the box is what the unit produces per hour under ideal conditions, but the real question is: how many litres do you need each day?
A rough guide for planning:
- Drinking and cooking only: 3 to 5 litres per person per day.
- Drinking, cooking, and basic hygiene: 8 to 15 litres per person per day.
- Showers, full galley, and guests: 20 to 40+ litres per person per day.
The Scout 10 LPH makes 10 litres per hour. Run it for two hours and you have 20 litres, more than enough drinking water for two people for a full day. The Scout 20 LPH doubles that and suits a small crew or modest daily consumption with less running time. If you need 80 to 200 litres a day, the Nomad is the right tool.
For help sizing precisely, the article How to Size a Watermaker System Properly walks through the calculation step by step.
The Scout: Best Reverse Osmosis Watermaker for Smaller Marine Craft
The LEDI Scout is designed for trailer sailers, cruising yachts from 20 to 50 feet, catamarans, and anyone who values portability. It weighs 18 kg, single-person carry, and requires no installation. Drop the stainless intake over the side, connect the supplied hoses, and the unit is making water within minutes.
Key specs at a glance:
- Output: 10 LPH or 20 LPH
- Power: 12V DC, 16 to 18 A draw
- Pump: Pumptec 107SS (USA), 316 stainless, approx. 800 PSI
- Salt rejection: 99.4% (output typically 250 to 300 ppm TDS)
- Pre-filter: 5 micron 2.5"x5" cartridge (replaceable)
- UV: built-in, post-membrane
- Hour meter: installed internally for service tracking
- Weight: 18 kg
- Feed water: handles seawater up to 35,000 ppm, plus brackish and river water
- Price: from $4,899 AUD
The Scout ships with a submersible feed pump. For longer hose runs (up to roughly 20 to 30 metres horizontally and 5 metres of vertical lift), either the Scout Auxiliary Feed Pump or the Nomad Auxiliary Feed Pump plugs straight in using the same SP13 2-pin connector, no adapter needed.
The Nomad: High-Output Marine RO for Bigger Boats and Crews
The LEDI Nomad suits liveaboards, charter boats, catamarans with larger crews, and anyone making 40 to 80 litres per hour. It runs a Cat Pumps 2SFSEEL 316-stainless high-pressure plunger pump, ships with an integrated control panel including a TDS monitor and flow meter as standard, and uses 2-stage pre-filtration. Like the Scout, it has an internal hour meter for service tracking.
The Nomad is portable but at 38 to 42 kg it is a two-person lift. It is available now, priced from $9,899 AUD for the single-membrane version and $10,899 AUD for the double-membrane. It runs on 12V or 24V DC.
For a deeper look at the Nomad's use cases, see the guide to High-Output Watermakers for Liveaboards.
Keeping a Marine RO System Running
A marine reverse osmosis watermaker needs basic but consistent maintenance. The pre-filter is the main consumable. On the Scout, that is a 5 micron 2.5"x5" cartridge, roughly $25 from the LEDI spares store. Replace it every 10 to 20 hours in silty or dirty water, or every 30 to 40 hours in clean ocean. If feed pressure climbs or output drops, change it sooner. The Scout also accepts an add-on 2.5"x10" pre-filter cartridge (larger, holds more dirt) which extends the time between changes and protects the membrane better.
The RO membrane is not a routine consumable. With a freshwater flush after every use and proper pickling for storage, it lasts several years. Only replace it when output or water quality genuinely declines. Full guidance on membrane care is in the article Watermaker Membrane Lifespan: What Shortens It and How to Make Yours Last for Years.
LEDI offers lifetime in-house servicing on the Gold Coast. Spare parts post Australia-wide and internationally, typically within one business day. Every wear part on both units is field-replaceable.
Why LEDI Over an Imported Marine Watermaker?
Fixed installed marine watermakers often cost $10,000 to $25,000 installed, not because the components are inherently more expensive, but because of import freight, overseas distributor margins, and specialist installation labour. LEDI builds on the Gold Coast, uses the same commercial marine-grade parts (non-proprietary and serviceable anywhere in the world), and ships direct. There is no overseas distributor between you and the manufacturer. When you call, you speak with a real person, not a call centre.
LEDI ships worldwide. Australian shipping is calculated at checkout. International freight is quoted case by case; contact the team at info@ledi.com.au or +61 494 562 668 for a quote. Import duties and taxes are the buyer's responsibility as determined by their country's customs.
Frequently Asked Questions
Can a marine watermaker run off solar panels alone?
Yes. The Scout draws 16 to 18 amps at 12V. A house battery bank supported by 200 to 400W of solar is enough to run it comfortably, with no generator needed. The Nomad draws more current, so larger solar and battery setups are appropriate for that unit.
What feed water can a marine RO watermaker handle?
LEDI watermakers are rated for seawater up to 35,000 ppm TDS and handle brackish and river water as well. Feed water temperature is rated up to 40 degrees C. Avoid harbours with heavy fuel or chemical contamination, as those require pre-treatment beyond a standard 5 micron cartridge.
How long does the RO membrane last in a marine watermaker?
With proper care, the membrane typically lasts several years. Flush with fresh water after every use and pickle the membrane when storing the unit for more than a few weeks. It is only replaced when output volume or water quality genuinely deteriorates, not on a fixed schedule.
Does LEDI hold CE or other certifications?
LEDI holds no formal certifications such as CE marking. If your order or region requires certification, contact the team directly at info@ledi.com.au and they can look into what may be possible for your situation.
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