Rainman Petrol (Gasoline) Watermaker

The original Rainman watermaker was our petrol (gasoline) powered system. In 2014, our first version of this system made the industry ask “Why didn’t someone think of a portable watermaker before this?”

This system requires no external power source, so long as you have fuel. It is ideal if you don’t have a generator and need to conserve your battery bank. Not relying on external power gives maximum flexibility for taking it ashore, loaning it out, or using it in emergency situations.

generator-driven watermaker

Power options

The heart of this system is the Honda GXH50 2.1HP engine, which is the same as that used in their 1kVA generator. It incorporates a tensioned belt drive system where the engine drives both an impeller lift pump and the General Pump high pressure pump. The fuel tank holds 700ml (1.5 pt) and will run for about 70 minutes, depending on fuel quality.

Benefits of petrol / gasoline power

Petrol (gasoline) exists on most boats already, so there’s good reason why you may consider using it to power your watermaker.

Some of the key benefits of using a separate motor for your watermaker include:

  • Simplicity:  For a portable configuration, there are only two boxes to set up and no need for external electricity.
  • Redundancy:  If your generator / inverter fails, you can still make water.
  • Efficiency:  There are no conversion losses between mechanical and electrical energy. Depending on water temperature, and source water salinity, you would expect a fuel to fresh water production ratio of about 150:1.
  • Security:  If you are in an urban survival situation after a natural disaster, a portable generator has very broad utility and greater chance of being stolen, rendering an AC system useless.
gasoline watermaker from rainman

Reverse Osmosis (RO) options

You have three options available for the reverse osmosis (RO) unit, depending on your water requirements, space available, and budget.

All three RO options are compatible with the petrol (gasoline) PSU and available in the protective cases. The fuel consumption and sound levels for the PSU are the same regardless of which RO unit is attached, so most customers will choose the High Output RO unit to get the most water made as quickly as possible.

High Output

• 100-140 lph (26-37 gph)
• 2 x 40″ RO Membranes

Our most common configuration with the AC system due to having the highest output and best overall value. Twice the output of the other options.


• 50-70 lph (13-18 gph)
• 2 x 21″ RO Membranes

A great option if you are physically space constrained. Also common if this is a backup system on a larger vessel as it can be stowed in smaller spaces.


• 50-70 lph (13-18 gph)
• 1 x 40″ RO Membrane

Our entry level water maker system is best suited for those on a budget. It can be upgraded to a high output system at a later date by adding a second membrane.

Fully self-contained watermaker

This system is perfect for those who don’t want to draw on their electrical system at all while topping up their water tanks.


  • 2.1HP Honda GXH50 (4 stroke) motor
  • 700 ml (1.5pt) fuel / 70 minutes operation
  • Integrated flexible impeller lift pump uses non-proprietary impeller
  • 2 meter (6 ft) maximum lift above sea level
  • General Pump WM 316 stainless steel high pressure triplex plunger pump
  • General Pump 316SS/ceramic relief valve to prevent overpressurisation
  • Sound levels: 73dB at 6 meters (20 ft)
  • Case of sturdy molded polyethylene
  • RO Case (mountable if desired): rotomolded polyethylene
  • Single 10″ x 2.5″ non-proprietary 5 micron pre filter to remove sediment mounted on PSU
  • 0 – 150lph (40gph) product water flow meter, integrated into RO case
  • 5 meter (16 ft) intake hose fitted with one way valve to remain primed, with detachable strainer
  • 3 meter (10 ft) brine waste discharge hose
  • PSU weight: 26kg (58lb)
  • PSU Dimensions: 600 x 375 x 270mm (23.6 x 14.8 x 10.6″)

Related RO weight:
– High Output: 23kg (51lb)
– Compact: 14kg (31lb)
– Economy: 11kg (24lb)

Related RO dimensions:
– High Output: 1,180 x 250 x 130mm (46.5 x 9.8 x 5.1″)
– Compact: 690 x 220 x 150mm (27.2 x 8.7 x 5.9″)
– Economy: 1,180 x 250 x 130mm (46.5 x 9.8 x 5.1″)

Optional accessories for your Rainman Watermaker


As the membranes age, the total dissolved solids of the product water increases. The Hydrotester measures nutrients, salts, and other dissolved solids to ensure that the quality of your water stays in top shape.

Spares & Consumables

While the Rainman system comes with enough spares and consumables to keep you going for a while, there are some items you’ll need over time to keep your system running for many more years to come.

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