Rainman Petrol (Gasoline) Water Maker


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 required 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.

gasoline water maker
installed petrol watermaker

Two Components – One Watermaker

The system is made up of a pressure supply unit (PSU) and a reverse osmosis unit (RO). Both parts are required to make a complete watermaker. The PSU lifts the seawater, filters out the sediment and puts the system under high pressure, while the RO unit extracts fresh water from the stream of pressurised seawater. Most of the water goes out to waste as brine output, while about 20% of the volume is extracted as fresh potable water for your tanks. Different RO options exist for you to select with your AC Rainman system, each to achieve their own specific objective.

rainman watermaker portable configuration


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.

rainman gasoline watermaker
saltwater desalinators petrol

Benefits of Petrol (Gasoline) Power

Petrol (gasoline)  exists on most boats already, so there is 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.
rainman watermakers

Reverse Osmosis 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 quick as possible.

More information about reverse osmosis »

saltwater desalinators gasoline


rainman petrol water maker

Features of Petrol (Gasoline) Watermaker

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 metre (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 metres (20 ft) – see chart
Case of sturdy moulded polyethylene
RO Case (mountable if desired): rotomoulded polyethylene
Single 10″ x 2.5″ non-proprietary 5 micron prefilter to remove sediment mounted on PSU
0 – 150lph (40gph) product water flow meter, integrated into RO case
5 metre (16 ft) intake hose fitted with one way valve to remain primed, with detachable strainer
3 metre (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″)
rainman petrol watermaker accessories

Optional Accessories

Since the petrol (gasoline) system must be run in a well ventilated area and should not be installed in your vessel, some of the options are not available with this system. One item that can be considered is a hydrotester to give you indication of the total dissolved solids (TDS), so you can know how your membranes are ageing.

Rainman desalinator optional accessories »

high output watermaker

Spares and Consumables

Your new Rainman system will arrive with enough spares and consumables to keep you going for a while, so most customers do not need to order more with initial purchase. There are a variety of items you will need over time to keep your system running for many years.

Rainman Watermaker spare parts and consumables »

rainman watermaker spare parts

AC System Options Gallery

rainman petrol water maker
Cased PSU

230VAC or 115VAC

high output desalination system
Cased High Output RO

2 x 40″ Membranes

compact cased watermaker desalination system
Cased Compact RO

2 x 21″ Membranes

high output desalination system
Cased Economy RO

1 x 40″ Membrane