Marine Watermakers for Sailboats
A reverse osmosis watermaker is one of the most liberating pieces of gear a cruising sailor can install — no more searching for water docks, rationing showers, or hauling jerry jugs. This guide covers every type, how to size one for your boat, what it takes to install it, and who makes the best systems.
💧 ElectroMax Marine Watermakers
ElectroMax has built a strong reputation among serious offshore sailors for producing compact, reliable, 12V and 24V DC watermakers that are designed from the ground up for marine use — not adapted from industrial or agricultural RO systems. Their units are known for quiet operation, quality membranes, and excellent customer support, including phone support from people who actually sail.
The company focuses specifically on sailboats and smaller powerboats, which means their mounting footprints, power requirements, and flow rates are sized for real-world cruising rather than spec-sheet marketing. Most of their systems can be run directly from solar or wind with a healthy battery bank.
ElectroMax 12 GPD
- 12 gallons per day
- 4–5 A at 12V
- Compact — fits in lockers
- Ideal for 1–2 person crew
- Solar-compatible
ElectroMax 30 GPD
- 30 gallons per day
- 8–10 A at 12V
- Good for 2–4 sailors
- Most popular model
- Run 2–3 hrs/day offshore
ElectroMax 60–75 GPD
- 60–75 gallons per day
- 14–18 A at 12V
- Larger crews or liveaboards
- 24V option available
- High-output membrane
📋 Types of Marine Watermakers
All marine watermakers use reverse osmosis (RO) — high-pressure seawater is forced through a semi-permeable membrane that blocks salt, bacteria, and most contaminants. The differences are in how the pressure is generated and where the power comes from.
⚡ 12V / 24V DC Electric
A 12V or 24V DC motor drives a high-pressure pump. The most popular choice for cruising sailboats because it runs directly from the ship's house bank — no separate AC circuit needed. Can be powered by solar, wind, or alternator.
- Runs off house batteries
- Solar & wind compatible
- Quiet operation
- Compact and modular
- No inverter needed
- DIY-installable
- Slower output than AC
- Draws 4–18 A continuously
- Battery bank must be adequate
- Lower GPD per $ than AC
🔌 110V / 220V AC Electric
AC-powered systems use shore power or a generator. They produce higher output for their size and cost, making them popular on larger cruisers and liveaboard boats that regularly connect to shore power or run a generator.
- High output per dollar
- Faster water production
- Simpler pump mechanism
- Lower up-front cost
- Needs generator or shore power
- Inverter needed at anchor
- Not suitable offshore
- Generator fuel cost adds up
- More noise when running
🛥 Engine-Driven (Belt or Hydraulic)
The high-pressure pump is driven by a belt off the engine or via a hydraulic circuit. Produces water when the engine is running — which offshore sailors often do anyway for battery charging. Very high output, no electrical load on the house bank.
- Very high output (50–300 GPD)
- Zero draw on house bank
- Runs while motoring anyway
- Long membrane life
- Complex installation
- Engine must be running
- Belt adds engine load
- Expensive to install
- Difficult to service at sea
💪 Manual / Hand-Pump
Human-powered units like the Katadyn Survivor series create RO pressure by hand pumping. Extremely low output (1–2 quarts/hour) and physically demanding, but essential as an emergency backup or ditch bag item for offshore passages.
- Zero power required
- Compact — fits ditch bag
- True emergency backup
- Inexpensive
- Very low output
- Physically exhausting
- Not practical as primary
- Membrane life limited
☀️ Solar-Integrated Systems
Some manufacturers offer DC watermakers designed to run directly from a dedicated solar panel array, completely separate from the house bank. Runs during daylight hours automatically, producing and storing water without any user interaction.
- Fully passive production
- No load on house bank
- Runs while you're away
- Environmentally clean
- Requires dedicated panels
- No water on cloudy days
- Higher overall system cost
- More complex wiring
📊 Side-by-Side Comparison
| Type | Typical Output | Power Source | Noise Level | Install Complexity | Best Use Case | Approx. Cost |
|---|---|---|---|---|---|---|
| 12V / 24V DC | 10–75 GPD | House battery bank | Low | Moderate — DIY-able | Offshore cruising | $800–$3,000 |
| AC Electric | 30–200 GPD | Shore power / generator | Moderate | Moderate | Liveaboard / marina use | $600–$2,500 |
| Engine-Driven | 50–300 GPD | Engine running | Moderate | Complex — pro install | Larger passage-makers | $2,500–$6,000+ |
| Manual / Hand | 1–4 GPD | Human power | Silent | None | Emergency backup | $200–$1,200 |
| Solar-Integrated | 15–60 GPD | Dedicated solar | Low | Moderate–complex | Anchored liveaboard | $1,500–$4,500 |
📐 How to Size a Watermaker for Your Boat
Start with your daily water consumption per person. A comfortable cruising sailor uses 2–4 gallons per day (drinking, cooking, minimal washing). Size your watermaker to cover a full day's supply in 2–4 hours of running time — not 24 hours, because membranes are happier running less than continuously.
Output needed by crew size — running 3 hrs/day:
🔧 Installation Requirements
A typical 12V DC watermaker installation on a 35–45 ft sailboat involves five main systems. Most experienced DIY sailors can complete the job in a weekend with the right tools and some planning.
🪣 Through-Hull & Sea Strainer
- Dedicated raw water intake through-hull (1/2" minimum)
- Seacock with a shut-off handle accessible underway
- 20–50 micron sea strainer before the pump
- Locate below waterline — avoid engine raw water intake
- Stainless or bronze through-hull only — never plastic on the low side
⚡ Electrical
- Dedicated circuit from the house battery bank
- Wire gauge sized for run length (typically 10–6 AWG)
- Inline fuse or breaker at the battery — 20–30A for most 12V units
- Tinned marine-grade wire throughout (no automotive wire)
- Adequate house bank: 200 Ah minimum for a 30 GPD unit
- Dedicated breaker on the panel — labeled clearly
💧 Plumbing & Product Water
- Inlet hose: 1/2" or 3/4" ID reinforced hose
- Product (fresh) water line to tank or tap
- Brine (reject) water overboard discharge — can T into existing drain
- Flow meter recommended to monitor output
- Product water should be tested with a TDS meter (<500 ppm is drinkable)
- Optional: carbon post-filter for taste improvement
📦 Unit Mounting
- Dry, ventilated locker — engine room or aft lazarette common
- Secure mounting to prevent vibration damage
- Access for filter changes and membrane service
- Keep away from fuel and bilge water
- Consider heat — RO membranes degrade above 113°F / 45°C
- Horizontal or vertical mounting per manufacturer spec
🧪 Pre-Filtration
- 20–50 micron sediment pre-filter (before high-pressure pump)
- 5 micron polishing filter (between sediment and membrane)
- Filter housings in an accessible location — you'll change them monthly
- Optional carbon pre-filter in polluted harbors
- Never run the unit in shallow, turbid, or polluted anchorages
🛡️ Pickling & Lay-Up
- Must be pickled (preserved) if not used for >3–5 days
- Use sodium metabisulfite solution per manufacturer instructions
- Flush with fresh water before pickling
- Flush preservative before producing drinking water
- Annual membrane inspection recommended
🗓 Maintenance Schedule
| Task | Interval | Notes |
|---|---|---|
| Inspect & clean sea strainer | Before each use | Clear any debris, weeds, or jellyfish |
| Check pre-filter pressure drop | Before each use | Replace if flow noticeably reduced |
| Replace 20-micron sediment filter | Monthly (more in turbid water) | Keep 3–6 spares aboard |
| Replace 5-micron polishing filter | Monthly–quarterly | Depends on water quality |
| Pickle the system | Any lay-up >3–5 days | Sodium metabisulfite solution |
| TDS (salinity) test of product water | Every run | Alert if TDS rises — membrane may need replacing |
| Flush with fresh water | After each use | Extends membrane life significantly |
| Inspect high-pressure hoses & fittings | Quarterly | Look for weeping or mineral deposits |
| Service high-pressure pump | Annually | Piston seals, check valves — per manufacturer |
| RO membrane replacement | Every 2–5 years | Depends heavily on use, water quality, and pickling discipline |
🏭 Leading Marine Watermaker Manufacturers
These are the most-referenced brands in the cruising community. All produce purpose-built marine systems — not adapted agricultural or industrial RO units.
ElectroMax
USA-made 12V and 24V DC watermakers designed specifically for cruising sailboats. Excellent phone support, quality membranes, and parts availability. A top recommendation for offshore sailors.
12V / 24V DC Offshore focus USA-madeSpectra Watermakers
Industry pioneer in energy-recovery DC watermakers. Their Clark Pump technology recycles reject water pressure, dramatically reducing power consumption. Popular on solar-powered cruising boats.
12V DC Energy recovery Solar-optimizedKatadyn (PowerSurvivor)
Best known for the Survivor 06, the SOLAS-approved hand-pump watermaker standard in offshore life rafts and ditch bags. Also makes small DC electric systems under the PowerSurvivor line.
Hand-pump 12V DC Emergency / smallVillage Marine Tec (Parker)
Produces a wide range of AC and DC watermakers, including high-output AC systems for larger vessels and charter boats. Also manufactures units for naval and commercial applications.
AC & DC High-output Commercial gradeSea Recovery
Italian manufacturer with a long history in marine and superyacht watermakers. Strong presence in the European cruising market. AC-dominant product line with some hybrid systems.
AC European market SuperyachtRainman
Australian brand known for portable, petrol (gasoline) engine-driven and AC watermakers. Popular in the Pacific and Australian cruising grounds. Self-contained units that don't require permanent installation.
Portable Gasoline engine ACSchenker
Premium Italian DC watermakers using patented energy-recovery Duo technology. Very low power draw for a given output — some models as low as 3.5 A for 20 GPD. A top choice for serious offshore passages.
12V DC Ultra-low power Energy recoveryHorizon Reverse Osmosis
Offers a wide range of compact DC and AC marine watermakers at competitive price points. Popular with budget-conscious cruisers and as a first watermaker for sailors stepping up from carrying water.
12V DC AC Budget-friendly📖 Glossary — Watermaker Terms
- RO (Reverse Osmosis)
- The membrane filtration process that separates salt from seawater under high pressure.
- GPD (Gallons Per Day)
- Output rated at a standard 77°F water temperature — real output in cold water will be lower.
- TDS (Total Dissolved Solids)
- Measured in ppm. Drinking water should be under 500 ppm; most watermakers produce 100–300 ppm.
- Brine / Reject Water
- The high-salinity discharge stream — typically 3–5 gallons of brine per gallon of fresh water produced.
- High-Pressure Pump
- The core component that pressurizes seawater to 800–1,000 psi to force it through the membrane.
- Clark Pump
- A patented pressure-exchange device (Spectra) that recycles reject water energy to boost efficiency.
- Pickling
- Preserving the membrane with a sodium metabisulfite solution when the unit won't be run for several days.
- Recovery Rate
- Percentage of feed water converted to product water. Typical marine units: 10–20% (low is normal).
- Pre-filter / Sediment filter
- Coarse and fine filters upstream of the membrane that prevent particulates from damaging it.
- Sea Strainer
- A basket strainer on the raw water intake that catches large debris before it reaches the pump.