Rainman · Watermaker

Rainman watermakers

Rainman watermakers are made by Rainman Technology in Sydney, Australia, and are meant to be as simple as a portable generator: a pressure supply unit (PSU) draws seawater in with an impeller lift pump, filters it to 5 micron and brings it to about 55 bar with a General Pump triplex plunger pump, and a separate RO unit turns roughly a fifth of it into fresh water. The first system, launched in 2014, was a self-contained Portable unit with a Honda GXH50 petrol engine; AC versions followed the same year and 12 V DC in late 2016, and there are now 24 V and 48 V DC versions as well. Since 2019 the same internals are also sold without cases as the Modular system (first called Naked) for fixed installation. The RO unit is named by its membranes (High Output 140L with two 2.5 × 40 in, Economy with one, Compact 70L with two 2.5 × 21 in), and electric PSUs changed in February 2019 from the Mk1 with the General Pump WM pump to the smaller Mk2 with the WMR, while petrol units keep the WM.

Manuals & documents

The links go straight to Rainman. We host no manuals or drawings — the manufacturer’s copy is the current one.

Wear parts & part numbers

PartOEM numberAlso fitsNote
Raw water pump impellerMI8131,4,5Jabsco 22405-0001-P1,2,3Johnson (SPX) 09-808B-13Lift pump impeller for every Portable and Modular system, petrol, AC and DC (only the Framed 240L Torrent takes a different one). Rainman names the Jabsco and Johnson impellers as equivalents; each new system ships with one spare.
Prefilter elementPU1296,7,8,9,10,11—10 × 2.5 in, 5 micron pleated sediment type, for all systems; dealer code, box of 24 PU129BOX. Any equivalent particle cartridge will do, but never a carbon or carbon/sediment one.
Reverse-osmosis membraneSW30-254012,1,13—2.5 × 40 in (Filmtec): two in the 140L High Output (AC, petrol, 48 V DC), one in the 75L Economy, 24VDC-55L and 12VDC-34L. Rainman’s current price list sells an Oltremare membrane of the same size. Fit it with the black brine seal at the upstream end.
Reverse-osmosis membraneSW30-252112,1,13—2.5 × 21 in (Filmtec): two in the 70L Compact RO, AC and petrol. Fit it with the brine seal at the upstream end.
Storage & cleaning chemicalsRM-PICKLE14,15,16—Pickling mix: 1 kg of food-grade sodium metabisulphite (SMBS), dealer code; a tub comes with every system. Rainman says the same powder from home-brew or wine-making suppliers does the job.
HoseRM-HP-HOSE-CAP-ASSY17,18,19—High-pressure hose PSU to RO, 5 m, with the RO end cap fitted; Rainman advises this version for older systems where the hose is hard to free from the round end cap. Its online hose guide tells you which version your system needs. Dealer code.
HoseRM-HP-HOSE-ASSY17,20,21—The same 5 m high-pressure hose with fittings but without the end cap, for Portable and Modular systems. Dealer code.
Valve kitWM0122,23,24—General Pump valve kit: six valve assemblies with O-rings, enough for all three cylinders. Rainman uses it for both the WM pump (petrol, Mk1 electric) and the WMR (Mk2 electric). General Pump also makes WM01E with EPDM O-rings; The Yacht Rigger sells the kit as PU175. Valve caps 30 Nm.
Pump seal kitWM0223,22,25—Packing kit for the WM pump: all petrol PSUs and Mk1 electric built to January 2019. Covers three cylinders and comes with General Pump’s seal tools; Rainman’s version (dealer code PU177-KIT) adds an extractor. Drips from the weep holes under the pump mean worn packings.
Pump seal kitRM0226,22—Packing kit for the WMR pump in Mk2 electric PSUs (AC and DC, built from February 2019). One source: The Yacht Rigger, dealer code PU261-KIT. Head bolts go back in at 12 Nm.
O-ring#11027—O-ring inside the PSU’s high-pressure quick-connect socket, 3/8 in ID × 9/16 in OD × 3/32 in. Replace it when the HP hose becomes hard to push in.
O-ringMI84728,29—End cap O-ring kit for the RO pressure vessels: 2 × BS116 and 2 × BS228 nitrile, for two end caps; grease them with food-grade grease when refitting. Dealer code, one source.
Bowl gasketPU20930—O-ring of the clear prefilter housing on the PSU, size #236 (3.250 × 3.500 × 0.125 in). Dealer code, one source.
Charcoal filter elementMI20031,1,32—10 × 2.5 in, only for the Autoflush kit, a control panel with flush or Framed systems: it takes the chlorine out of tank water before the flush. Never use it as the seawater prefilter. Dealer code, one source (another dealer lists it as M1200).
Drive beltPP18433,34,35—Double-sided toothed belt for petrol PSUs built from mid-2016 (tensioned pulley). Older petrol units use a single-sided belt, so say which when ordering; electric PSUs have no belt. Dealer code.
Spark plugCR5HSB36,37Denso U16FSR-UB36,37NGK plug for the Honda GXH50, petrol PSU only; gap 0.60–0.70 mm.
Salinity testerCOM-8038,1,39—HM Digital COM-80 handheld TDS/EC meter (hydrotester), sold by Rainman as an option for all systems: it checks product water and shows when the membranes are due, at about 700–800 ppm.
Service kitRMSK10040—Annual supply kit: 8 prefilters (5 micron), pickling mix, a spare impeller, 2 pints of pump oil and a TDS meter; suits every system except the Torrent. One source (The Yacht Rigger).

Numbers checked against the sources below on 13 October 2026. Always confirm against your serial number and exact type before ordering.

Service intervals

TaskInterval
Fresh-water washUnused 2 to 7 days: flush with about 10 l of chlorine-free product water, pressure valve fully open. The optional Autoflush does this every 7 days; change its carbon filter every 6 months41,32
Storage / winterisingUnused 7 to 30 days: pickle with 1 % SMBS (3 scoops of 29 ml in 10 l of fresh water); over 30 days also discard the prefilter and drain its housing. Keeps up to 12 months; if it may freeze, use propylene glycol (30 % down to −15 °C, 50 % down to −40 °C)41,42
Prefilter changePrefilter cartridge: replace when visibly fouled, typically after 5 to 50+ h depending on the water; always fit a new one when recommissioning after more than a month pickled41,43
Raw water impellerEvery year or 500 h, and whenever the system has been pickled for more than 6 months41,42
Oil level checkHigh-pressure pump oil: check the sight glass from time to time and change yearly (Rainman); General Pump’s WM manual says first change after 50 h, then every 300 h or 3 months41,44
RO membraneRO membranes: no fixed interval, they typically last 5 to 10 years; change them when product water reaches about 700–800 ppm TDS12
Engine oil changeHonda GXH50 (petrol PSU): check before each use; change after the first month or 10 h, then every 6 months or 50 h (every 25 h under heavy load or in high heat)37
Air filterHonda GXH50: check before each use; clean every 3 months or 25 h, more often in dust37
Spark plugHonda GXH50: clean and adjust every 100 h; replace every 2 years or 300 h37
Valve clearanceHonda GXH50: check and adjust every 2 years or 300 h; Honda leaves this to a dealer37

From Rainman’s petrol and electric operations guides, its Autoflush guide, membrane page and spare-parts page; the second half of the pump-oil row is General Pump’s schedule for the WM series. Rainman’s own care is mostly by condition: flush or pickle according to how long the unit stands, change the prefilter when it is dirty. The Honda rows apply to the petrol PSU only and come from the Honda GXH50 owner’s manual.

Specifications

Years builtSince 2014: petrol launched at the 2014 Sanctuary Cove Boat Show, AC electric later in 2014, 12 V DC late 2016, Mk2 electric and Naked (now Modular) 201945
TypeReverse-osmosis watermaker in two units: pressure supply unit (PSU) with impeller lift pump, 5 micron prefilter and General Pump triplex plunger pump, driven by a Honda GXH50 through a belt or by an AC/DC motor; RO unit with the membrane pressure vessels, pressure control needle valve, gauge and flow meter46,22
Models140L High Output (two 40 in membranes): 100–154 l/h (26–41 gph), AC or petrol · 75L Economy (one 40 in): 55–82 l/h (15–22 gph), AC or petrol · 70L Compact (two 21 in): 50–77 l/h (13–20 gph), AC or petrol · 48VDC-140L (two 40 in): 100–154 l/h · 24VDC-55L (one 40 in): 45–61 l/h (12–16 gph) · 12VDC-34L (one 40 in): 26–37 l/h (7–10 gph). Formats: Portable (in cases) or Modular; petrol only as Portable1
VersionsPortable: PSU and RO each in a case, can also be installed · Modular (released 2019 as Naked): the same internals without cases · Electric PSU Mk1 (to January 2019): WM pump with separate VS100 relief valve · Mk2 (from February 2019): WMR pump with integrated relief valve, 30 % smaller · Petrol: always the WM pump with VS100; single-sided drive belt before mid-2016, double-sided after; the first 30 units had a fibreglass shell45,22,33
Flow rateMaximum product flow, never to be exceeded (watch it in brackish or rain-diluted water): High Output 140 l/h (37 gph) · Compact and Economy 70 l/h (18 gph) on AC and petrol · 12 V DC Economy 34 l/h (9 gph)41,42
Operating pressureOperating pressure 55 bar (800 psi) in seawater, 51–58 bar (750–850 psi) acceptable, never above 58 bar (850 psi). Relief valve starts to open at about 62 bar (900 psi), fully open at about 69 bar (1000 psi), factory set41,22
Power consumptionAC: 1250 W, about 6 A at 230 V or 12 A at 115 V · 48 V DC: 1250 W, 26 A · 24 V DC: 600 W, 24 A · 12 V DC: 400 W, 30 A (up to 40 A briefly at start, 28–32 A once warm)1,47
EnginePetrol PSU: Honda GXH50, 49 cc four-stroke OHV single, 1.6 kW (2.1 bhp) at 7000 rpm, air-cooled; drives the lift pump and the HP pump through a tensioned belt36,46
FuelUnleaded petrol; Rainman recommends premium fuel without ethanol41
Fuel tankRainman: 700 ml, about 70 minutes of running · Honda: 0.77 l in the current GXH50 manual, 1.2 l in the older manual Rainman hosts46,36,37
Fuel consumptionAbout 1 l of petrol per 150 l of fresh water, depending on water temperature and salinity46
Engine oil capacityHonda GXH50: 0.25 l, SAE 10W-30 (API SJ or later). Rainman’s first-use instruction says to fill 200 ml of 10W-30 or SAE 3036,41
LubricationHigh-pressure pump: SAE 30 oil (any xW-30 such as 5W-30, 10W-30, 15W-30; ISO 100); General Pump specifies SAE 30 non-detergent. Refill quantity differs by source: Rainman 350 ml (petrol guide), 330 ml (electric guide), 300 ml (spares page); General Pump 12 oz crankcase capacity for the WM series41,42,43,23,44
Suction / discharge headPSU no more than 2 m (6 ft) above the water; it works best close to water level1,42
Inlet hosePortable: 1/2 in ID intake hose with one-way valve and detachable strainer, 5 m on electric and 3 m on petrol units1
Discharge hosePortable: high-pressure hose PSU to RO 1/4 in, 5 m (16 ft), 10 m to special order · product water 8 mm OD, 3 m plus a 10 m extension · brine 10 mm OD, 3 m1
WeightPortable: AC-140L 47 kg, AC-75L 35 kg, AC-70L 38 kg, 24VDC-55L and 12VDC-34L 35 kg, Petrol-140L 49 kg, Petrol-75L 37 kg, Petrol-70L 40 kg · Modular: AC-140L 45 kg, AC-75L 33 kg, AC-70L 36 kg, 48VDC-140L 46 kg, 24VDC and 12VDC 33 kg1
DimensionsPortable PSU 600 × 375 × 270 mm (AC/DC), 595 × 450 × 310 mm (petrol); Portable RO 1180 × 250 × 130 mm (40 in), 690 × 220 × 150 mm (70L Compact) · Modular PSU 470 × 270 × 240 mm (AC), 470 × 230 × 240 mm (DC); Modular RO 1170 × 220 × 120 mm (40 in), 670 × 220 × 120 mm (70L)1
Sound levelMeasured at 6 m: AC 62 dB, 12/24 V DC 58 dB, 48 V DC 59 dB, petrol 73 dB1
Warranty2 years from shipment; consumables (prefilters, impeller, pump oil, packings, HP hose, engine oil, membranes) excluded. The Honda engine has Honda’s own 3-year warranty41

Good to know

  • Never let chlorinated water reach the membranes: no shore tap water and no treated tank water. Flush only with the watermaker’s own product water, or through the Autoflush carbon filter.41,32
  • Use a plain 5 micron sediment cartridge as the prefilter. Carbon or carbon/sediment cartridges, even when labelled 5 micron, choke the flow and make the high-pressure pump cavitate.47,41
  • A shaking HP hose, a fluttering gauge or no way to reach 55 bar almost always means a starved pump: replace the prefilter (rinsing is not enough), check the impeller, keep the PSU within 2 m of the waterline and look for air leaks in the intake hose and its check valve.47
  • Do not make the pickling mix stronger than 1 %: strong SMBS swells the lift-pump impeller and the seal ring in the intake check valve (20 mm across when new, replace it above 22 mm) and corrodes. Keep the SMBS tub sealed and stored away from the unit in a dry, ventilated place.47,41
  • Bring the pressure up gradually (Rainman says about a minute to reach 55 bar on the electric units, no more than 20 bar a minute on the petrol unit) and open the valve to below 20 bar before switching off. In brackish or rain-diluted water, watch the flow meter and stop at the rated maximum flow.42,41
  • Before ordering pump parts, check which pump you have: petrol units and Mk1 electric units built to January 2019 have the General Pump WM with a separate VS100 relief valve, Mk2 electric units from February 2019 the WMR with the relief valve in the manifold. The valve kit WM01 fits both, the packing kits differ (WM02 or RM02).22,26

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Sources

  1. rainmandesal.com/watermaker-comparison/
  2. rainmandesal.com/lift-pump-impeller/
  3. rainmandesal.com/impeller-maintenance/
  4. theyachtrigger.com/products/rainman-replacement-lift-pump-impeller
  5. mareamarine.com/products/rainman-impeller-replacement-portable-and-modular
  6. rainmandesal.com/watermaker-prefilter-cartridges/
  7. theyachtrigger.com/products/rainman-prefilter
  8. mareamarine.com/products/rainman-5-micron-prefilter-cartridge-2
  9. riggingshoppe.com/products/rainman-carbon-prefilter-5micron
  10. theyachtrigger.com/products/rainman-prefilters-24-pack
  11. mareamarine.com/products/rainman-5-micron-prefilter-cartridge-box-of-24
  12. rainmandesal.com/reverse-osmosis-membranes/
  13. thewetworks.co.uk/products/rainman-spare-reverse-osmosis-membranes-21-53cm-or-40-101cm
  14. rainmandesal.com/watermaker-pickling-solution/
  15. theyachtrigger.com/products/rainman-pickling-solution-mix-1kg-2-2lb
  16. riggingshoppe.com/products/rainman-carbon-filter-5micron
  17. rainmandesal.com/high-pressure-hose/
  18. theyachtrigger.com/products/rainman-hp-hose-replacement-assembly-cap
  19. mareamarine.com/products/rainman-5-micron-prefilter-cartridge
  20. theyachtrigger.com/products/rainman-hp-hose-5m
  21. mareamarine.com/products/rainman-5-metre-high-pressure-hose-without-end-cap
  22. rainmandesal.com/rainman-high-pressure-pump-service/
  23. generalpump.com/product/wm1015c/?attachment_id=104323&download_file=43d1c902bbf4f8ccf1e75…
  24. theyachtrigger.com/products/rainman-gp-wm01-valve-kit
  25. theyachtrigger.com/products/gp-packing-kit-wm-kit
  26. theyachtrigger.com/products/gp-packing-kit-wmr
  27. rainmandesal.com/quick-fit-o-ring-replacement/
  28. theyachtrigger.com/products/rainman-end-cap-o-ring
  29. rainmandesal.com/change-reverse-osmosis-membranes/
  30. theyachtrigger.com/products/rainman-prefilter-spare-o-ring
  31. theyachtrigger.com/products/carbon-prefilter-cartridge-5-micron
  32. rainmandesal.com/rainman-autoflush-system-guide/
  33. rainmandesal.com/petrol-watermaker-drive-belt/
  34. theyachtrigger.com/products/rainman-petrol-gasoline-drive-belt
  35. riggingshoppe.com/products/drive-belt-v1-double-sided-teeth
  36. cdn.powerequipment.honda.com/engines/pdf/manuals/37Z4C603.pdf
  37. rainmandesal.com/wp-content/uploads/2018/09/honda-gxh50-manual.pdf
  38. rainmandesal.com/watermaker-price/
  39. theyachtrigger.com/products/rainman-hydrotester-1
  40. theyachtrigger.com/products/annual-rainman-supply-kit-1
  41. rainmandesal.com/petrol-operations-guide/
  42. rainmandesal.com/electric-watermaker-operations-guide/
  43. rainmandesal.com/water-maker-spare-parts/
  44. generalpump.com/product/wm1015c/?attachment_id=10270&download_file=5af483318acda
  45. rainmandesal.com/rainman-desalination-story/
  46. rainmandesal.com/petrol-water-maker/
  47. rainmandesal.com/watermaker-troubleshooting-support/

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