rainman portable watermaker logo


True portability – The gasoline rainman watermaker utilizes an onboard honda GXH 50 engine to mechanically drive the internal pumping components. 1/4 gallon of gasoline will operate the system for over an hour – enabling the production of up to 37 GPH of freshwater when paired with the Rainman Watermaker high output case.

Gasoline Systems are capable of up to

37 GPH


Rainman Watermaker

Pressure Supply Unit (Gasoline PSU)

Two Components – One System

The Rainman Watermaker consists of two components: the Pressure Supply Unit and a set of Reverse Osmosis Membranes. Both are required to make a complete Rainman Watermaker desalination system. 

The Pressure Supply Unit is easily selected based upon your power supply onboard – so in this case no external would be required, as the system operates from its onboard 50cc honda GXH 50 Engine . The PSU lifts the seawater, filters out dirt and sediment then puts the system under high pressure for operation. A set of membranes are connected to the PSU to extract drinking water from the seawater  – which is the basic operation of the system.


Gasoline Pressure Supply Unit

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.


Technical Specifications

  • 2.1 HP Honda GXH50 (4-stroke) engine
  • 1/4 Gallon Gasoline = 70 Mins Operation
  • 16ft Intake hose with strainer 
  • Integrated flexible impeller
  • 6ft maximum vertical lift above sea level / source water
  • GP WMR 316 stainless steel high pressure triplex plunger pump 
  • Integrated GP 315SS Ceramic relief valve to prevent overpressurisation.
  • Sound level – 73dB at 20ft 
  • Rotomoulded polypropylene case
  • PSU storage / mounting seat included

PSU Dimensions

  • PSU Weight 58lbs
  • L23.4″ x H17.7″ x D12.2″

Rainman Watermaker

Membrane Options

Two Components – One System

The Reverse Osmosis Membrane is ‘Part Two’ that will complete your Gasoline Rainman Watermaker Desalination System.
Membrane selection is a combination of size and product water requirements.
The membranes are available in three options: Economy, Compact and High Output. The intentional naming of the membrane options represent the selection characteristics
The membranes recieve the high pressure water from the Pressure Supply Unit and, using reverse osmosis, extract the drinking water from the seawater.
The membranes will produce two ‘output’ streams – the first will be the ‘Brine’ or ‘Waste water’ – which you will discharge back into the ocean – this is simply the same water that came in to the system – minus some pure water molecules.
The second stream the membranes produce is the ‘permeate’ or ‘fresh water’ stream. This is the output that we commonly refer to as ‘product’ water, and is comparable in quality to bottled or distilled water. You will place this product water hose in your fresh water tanks and leave to fill.

High Output Membranes

26 – 37 GPH

The high output membrane is the flagship model – designed specifically for the Rainman Gasoline  Pressure Supply Units. With the High Output Case, you can expect to produce between 26 – 37 GPH. This is our most popular and highest output option.

  •  Compatible the Gasoline PSU
  • Produce Up To 37 Gallons Of Drinking Quality Water Per Hour.
  • Desalinate Sea, Brackish and Fresh water 
  • Twin 40″ Dupont Filmtec Membranes
  • Robust Polyethylene Case
  • 10ft Brine Discharge Hose
  • 10ft Product Water Hose + 33ft Extension
  • 16ft High Pressure hose (PSU connection)
  • Length – 46.6″
  • Depth – 5.1″
  • Height – 9.8″
  • Weight – 52lbs
  • 2 Year Rainman Warranty
  • Preffered Seatask Support 


13 – 18 GPH

An ideal companion for the Gasoline PSU if you are short on space, and do not require the higher output that the High Output membrane provides. This compact case, together with the Rainman Gasoline PSU is capable of producing between 13 – 18 Gallons Per Hour.

  • Compatible with the Gasoline PSU
  • Produce Up To 18 Gallons Of Drinking Quality Water Per Hour.
  • Desalinate Sea, Brackish and Fresh water 
  • Twin 21″ Dupont Filmtec Membranes
  • Robust Polyethylene Case
  • 10ft Brine Discharge Hose
  • 10ft Product Water Hose + 33ft Extension
  • 16ft High Pressure hose (PSU connection)
  • Length – 27.2″
  • Depth – 5.9″
  • Height – 8.7″
  • Weight – 32lbs
  • 2 Year Rainman Warranty
  • Preffered Seatask Support 


13 – 18 GPH

The most economical companion to the Gasoline PSU. With the Economy Membrane, you can expect production rates between 13 – 18 Gallons Per Hour.

  • Compatible with the Gasoline PSU
  • Produce Up To 18 Gallons Of Drinking Quality Water Per Hour.
  • Desalinate Sea, Brackish and Fresh water 
  • 40″ Dupont Filmtec Membrane
  • Robust Polyethylene Case
  • 10ft Brine Discharge Hose
  • 10ft Product Water Hose + 33ft Extension
  • 16ft High Pressure hose (PSU connection)
  • Length – 46.6″
  • Depth – 5.1″
  • Height – 9.8″
  • Weight – 23lbs
  • 2 Year Rainman Warranty 
  • Preffered Seatask Support 


We accept all methods of payment, but we have also partnered with affirm to offer a range of financing options!

Click below to learn more.

Rugged and Robust

Rainman Watermakers are solid and robust portable desalination systems – designed for the rigors of the maritime environment and built with ingenuity, with the rainman gasoline systems being completely independent, and backed by the global and prestigious Rainman and Honda warranty. Check out the videos below to see out most popular portable desalination systems in action and why you too will love the Rainman Watermaker System.



Looking for assistance in selecting your watermaker? Use our system selection guide

for step by step guidance in selecting your perfect Rainman Watermaker System.

Less Than 10 Minutes

The Rainman Watermaker – portable configuration – comes ready to operate out of the box. With the first time set up of your portable desalination in as little as 10 minutes, you can benefit from a fully functional, and extremely robust portable desalination system right away – without the cost, downtime or complexity of installation.

Portable Desalination Rainman watermaker operations

Can The Rainman Gasoline System Be Used As A Generator?

No! The rainman gasoline watermaker is powered by a honda engine – which mechanically drives the pumps via a drive belt system – this does not produce electricity, and more importantly, keeps the energy purely mechanical to maximise system efficiency. 

Do I Have To Buy Spares Through Rainman / Seatask?

No! The Rainman Watermaker system uses components that are compatible with many other brands – and the sizing of the membranes and filters are common size – which means that you can source from various marine stores globally.

What is The Lead / Shipping Times? Shipping Costs?

We offer a flat rate shipping cost of $330 throughout the USA. PR / VIs and Caribbean usually runs around $550. We ship all systems within 24 hours of order by UPS – with an average delivery time of around 5-7 business days.

What Is The Maintance Required on A Rainman System?

All systems onboard require maintance – your watermaker is no exception. A full guide comes with your system – but as a rule of thumb:


  •  5-50 Hrs – Prefilter Change
  • 1-2 Years – Impeller & Oil Change
  • 5-10 Years – Membrane, Packings and drivebelt Change

Are There Any Current Promotions?

We have a number of promotions available throughout the year on systems and spares. Sign up to receive our monthly promotions emails here… (When you purchase your system through Seatask – you receive a discount on service and spares purchased from our store.)

Where Can I Request Information?

Select your system with our interactive selection tool, and we’ll send you a brief email with details, pricing and specifications – plus a direct contact for questions to our team. 



Thank you to our customers for taking the time to send in and record there experiences with there Rainman Watermakers!

Our Customers



“My experience with Seatask and the rainman watermakers has been excellent. Chrstopher Burton was extremely helpful and responsive in every step of the purchase/deliver/setup. He helped me figure out what I needed and shipped it quickly. The unit itself is great. Easy to setup, easy to use and exactly what we needed (a reliable, portable watermaker to extend our cruising range and reduce reliance on shoreside solutions in the Caribbean). Will likely buy another one next year for our fleet. I highly recommend this company and product..”

Having a 4kw generator made the electric high output unit the best choice for us. The portable aspect was the clincher, not having to install parts and pieces was the second most important issue. Taking the water maker off the boat for the several months when we don’t cruise, and storing it in a closet at home, is huge. It was extremely easy to lift the unit out of the lazarette, set it on the deck and drop the hoses overboard.

We spent 3 months in the Exumas Bahamas this past winer and unlike last year when we had to continually go to the dock to take on water we were able to produce our own water using the Rainman RO system. It worked beyond our expectations and produced water at about 30 gallons per hour. We hold 500 gallons and never ran out of water even with multiple guests on board. This product has saved us thousands by not having to install a permanent system on our boat and it is portable so other boats that travel with us are also able to produce water due to how portable it is. We are very happy with our choice to get the Rainman RO system.

Chris and his team did a great job helping us with getting our unit through French Customs in La Rochelle. We used our Rainman watermaker on a daily basis as we spent forty days total (thirty at sea) crossing the Atlantic from La Rochelle to Tortola BVI. We had six on board and so each day we’d top up our tank averaging 150 litres a day which took the rainman about 11/4 hours to make from beginning to end. The system is simplicity itself and after the first couple of times became just a routine of life on board. Our skipper who has fought and lost with many types of watermaker was most impressed.

Complete Supply Kit

Each system purchased through Seatask comes complete with a supply kit of filters, strainer, pickling solutions and manuals – enough to allow you to have a fully functional and ready to use system and consumables right out of the box. (2 Months Supply)

As Featured In..

Rainman systems have been featured in countless articles, blogs, websites, youtube videos and have would numerous awards. This experience and global coverage ensure that you are investing in quality, reputable equipment – stood behind by a wide network of support personel, dealers and staff.

Get In Touch

+1 (305) 965-8775



Walk In’s / Store / Pickups suspened until further notice.

Ft Lauderdale
Florida, 33334




Office / Phone Hours

Mon:10am – 4pm
Tue: 10am – 4pm
Wed: 10am – 4pm
Thur: 10am – 4pm
Fri: 10am – 3pm
Sat: 10am – 1pm
Sun: Closed

Send A Message

    Your Cart
    Your cart is emptyReturn to Shop
      Calculate Shipping
      Apply Coupon