Choosing a Watermaker or Water Purifier for a Boat in Thailand

There are two different problems that bring people to this page. One is tankage: the boat goes cruising and the water runs out before the holiday does. The other is spots: every wash-down in a Thai marina dries to a film of calcium on the glass and the gelcoat, and the crew spend their afternoons with chamois. Both have the same answer in principle — reverse osmosis — but they are different machines, and the first decision is which one you are actually buying.

On this page

1. Watermaker, purifier or both
2. Sizing: litres per day, then litres per hour
3. What Thai waters change
4. Power: 50 Hz, generators and inverters
5. Space and installation
6. What it costs, and what it costs to run
7. Automatic or semi-automatic
8. How we supply Spot Zero in Thailand
9. Frequently asked questions
10. Size it in two minutes

Watermaker, purifier or both

	Watermaker (SeaXchange)	Water purifier (Spot Zero)	Combination (XZ II)
Feed	Seawater	Dock water or watermaker output	Seawater and dock water
Output	Fresh water for tanks, showers, galley	Spot-free wash-down and bottled-quality water, about 10 ppm	Both, from one frame and one screen
Solves	Running out of water at sea	Water spots, scale, bottled water on board	Everything above
Who buys it	Cruising boats, charter, liveaboards	Marina-based boats of any size; crews who detail	Yachts that cruise and want the finish kept
Capacity	600–2,200 GPD (XTC II / SX III); next generation to 6,000 GPD	1,000–3,000 GPD built-in; Mobile Pro and Mini portable	900–2,200 GPD seawater with 1,000–3,000 GPD purifier

If the boat lives in a marina and the complaint is spots, start with a purifier — portable if you move berths or want it off the boat, built-in if you want the water at every tap. If the limit is tankage, it is a watermaker. If it is both, the XZ II is cheaper than two separate systems and takes one installation. Our parts and service guide covers what each one costs to run.

Sizing: litres per day, then litres per hour

Capacity is quoted in US gallons per day (GPD), which assumes 24 hours of running. Nobody runs a watermaker all day, so the number that matters is litres per hour against the hours you are willing to run the generator. A 600 GPD system makes about 95 litres an hour; a 1,200 GPD system about 190; a 2,200 GPD system about 350. Work out the boat’s daily use, decide the run time, and pick the capacity that covers it with a margin:

• People. As planning figures we use 60 litres per person per day for a frugal crew, 120 for comfortable cruising and 200 for guests who expect long showers.
• Wash-downs. A proper rinse of a 50 ft boat uses a few hundred litres; a superyacht wash-down, thousands. If the wash-down water is to be spot-free, that is purifier capacity, not watermaker capacity.
• Margin. We add 15 % for 50 Hz operation and membrane ageing, so the system is not running flat out from day one.

The watermaker sizing calculator turns those into a daily litres figure, the litres-per-hour you need for your run time, and the Spot Zero capacity that fits.

What Thai waters change

Warm seawater is on your side. Reverse-osmosis output is rated at a standard temperature and salinity, and in 29 °C Andaman or Gulf water a membrane passes more water than in the cold conditions it is rated in — one of the few things in boat ownership that gets easier in the tropics. Two things to plan for instead: harbour water after rain carries silt, so pre-filters work harder and you keep spares; and most Thai marinas supply hard water, which is why the purifier is the half of the system owners here notice every day.

Power: 50 Hz, generators and inverters

Thailand is 230 V 50 Hz. Spot Zero builds for 50 or 60 Hz; the XTC II watermaker draws up to about 14 A at 230 V, the ZTC II purifier 5 A, and the XZ II about 5 A at the dock and 19 A at sea with both stages running. Spot Zero notes that production can be slightly lower at 50 Hz, which is the margin above. A 6–8 kVA generator runs any of the single-phase systems comfortably; a large lithium bank with a 3–5 kW inverter can run a purifier or a smaller watermaker for an hour or two at anchor. The Mobile Pro Mini is 110–120 V 60 Hz only and runs here from a step-down transformer; the Mobile Pro is available in 230 V.

Space and installation

Every Spot Zero built-in system is drawn in local and remote-mount versions: the control unit is a box about 570 × 310 × 325 mm, and the membrane vessels — 1.2 m long for the 40-inch elements, 0.7 m for the 21-inch — can be on the unit or anywhere a straight run fits, with the pre-filters mounted where they can be reached. The full dimensions, weights, plumbing sizes and wiring diagrams are on each system’s product page, and we send the CAD with the quote. The one rule that is not negotiable: the seawater boost pump goes below the waterline.

What it costs, and what it costs to run

Spot Zero’s US list prices start at US$20,400 for the automatic XTC II watermaker, US$15,400 for the semi-automatic SX III, US$14,000 for the ZTC II purifier, US$10,400 for the SZ III and US$32,000 for the XZ II combination; the Mobile Pro is US$6,999 and the Mobile Pro Mini US$4,999. We list the mobile units and all parts at those prices and quote built-in systems per boat; freight is at cost. Running costs are the consumables: a season of pre-filters, a flush cartridge, a bottle of storage solution, and membranes every few years.

Automatic or semi-automatic

The XTC II and ZTC II run from a 7-inch touchscreen: push to start, automatic pressure regulation, automatic fresh-water flush, NMEA 2000 and a second screen at the helm if you want it. The SX III and SZ III do the same work with an LCD keypad and a hand on the pressure valve, for about a quarter less. For an owner-operated boat the automatic systems are worth it; for a crewed boat with an engineer who likes to see the gauges, the semi-automatic versions are a sensible saving.

How we supply Spot Zero in Thailand

Drake Marine supplies the range as a factory-direct purchase with our support around it: we size the system, specify the 50 Hz configuration, handle the technical questions with Fort Lauderdale, support commissioning with your yard, register the warranty, and keep the parts coming from Thailand. Tell us the boat, the tankage and where she lives — LINE @drakeco, WhatsApp or email — and we will come back with a capacity and a quote.

Frequently asked questions

What is the difference between a watermaker and a water purifier?

A watermaker (marine desalinator) turns seawater into fresh water with a seawater reverse-osmosis membrane and a high-pressure pump. A water purifier takes fresh water — from the dock or from the watermaker — through a second, fresh-water reverse-osmosis pass and brings it down to about 10 ppm, which is water that dries without spots and is cleaner than bottled water. Spot Zero makes both, and the XZ II puts them in one frame.

How big a watermaker does my boat need?

Add up the people aboard times their daily use, the showers, the galley and the wash-downs, then decide how many hours a day you are willing to run the system, and that gives the litres per hour you need. As a planning figure, most cruising yachts of 40–70 ft land between 600 and 1,200 US gallons a day (2,300–4,500 litres) of rated capacity. Our watermaker sizing calculator does the arithmetic.

Does a watermaker work on 50 Hz power in Thailand?

Yes. Spot Zero builds its systems for 50 or 60 Hz, single-phase 230 V (115 V on some purifiers) and three-phase on the Super Yacht models. Spot Zero notes that production can be slightly lower at 50 Hz because the pump motor turns a little slower, so we size a Thai installation with that margin built in.

How much does a watermaker cost?

Spot Zero’s US list prices start at US$20,400 for the SeaXchange XTC II automatic watermaker, US$15,400 for the semi-automatic SX III, US$14,000 for the ZTC II purifier and US$32,000 for the XZ II combination; the Mobile Pro purifier is US$6,999 and the Mobile Pro Mini US$4,999. Built-in systems are quoted per boat on capacity and configuration, with freight to Thailand at cost.

Can I run a watermaker at anchor without a generator?

The Spot Zero range runs on AC, so it needs the generator, the shore supply or an inverter sized for the running load — around 14 A at 230 V for the XTC II. On a boat with a large lithium bank and a 3–5 kW inverter it is realistic to make water on batteries for an hour or two; tell us the electrical system and we will advise.

Why do I get water spots after washing the boat in a Thai marina?

Because the dock water is hard: it carries dissolved calcium and other minerals that are left behind when a drop dries. Softening does not help (the sodium spots too). Only removing the dissolved solids — a reverse-osmosis purifier — gives water that dries clean, which is what the Spot Zero mobile and built-in purifiers do.