Buying a used watermaker: what to check

Ask these before you look at it

1. When was it last run, and for how long? A system run monthly is in a different condition to one that sat for two seasons, regardless of hours on the clock.
2. Was it pickled before it was laid up, and with what? This is the question. An unpickled system that sat wet has a biologically fouled membrane, and possibly a ruined one.
3. What is the membrane's age, and is there a service history? Five to ten years is normal life with care; two is normal without it. Dates matter more than hours.
4. Why is it being sold? A boat sale is a good reason. “It stopped making good water” is a reason to find out what was diagnosed and what was not.

What to inspect

• The high-pressure pump. Look for salt crust, weeping seals and corrosion at the head. Pumps are rebuildable, so this is a price negotiation rather than a deal-breaker — if a kit is available.
• The pressure vessel and end caps. Corrosion or cracking here is more serious and less cheaply fixed than the pump.
• Hoses and fittings. High-pressure hose has a service life and perishes from the inside. Assume replacement on anything old and budget for it.
• The control panel and wiring. On automatic systems this is where age shows. Ask whether the controller is still supported and whether parts exist.
• Completeness. Missing brackets, the original manual, the flush kit and the correct fittings all cost real money and time to reassemble.

Price it against new, properly

Work out what the same output and efficiency costs new, then subtract what you will spend making the used one right: membrane if its history is unknown, pump seals, hoses, and a service. If the gap is small, buy new and get a warranty and a supported product.

Also check the brand is supported here before you commit. A cheap used system from a brand with no Australian parts channel is a system you cannot fix, and freight on a pressure vessel is not trivial.