Watermaker installation: what it involves and what to ask

What the job consists of

• A dedicated raw-water intake. Its own skin fitting, seacock and strainer, below the waterline and forward of anything that discharges. Sharing the engine intake is the common shortcut and the common cause of air locks.
• A brine discharge. Above the waterline where you can see it running — that visible stream is your first diagnostic every time you start the system.
• The unit's mounting. Rigid, dry, ventilated, and reachable. You will change a prefilter every few weeks and open the membrane housing once a year.
• The power run. Cable sized for the length of the run, its own breaker, and a solid connection to the bank. On AC, whether it will start on your inverter or needs shore power and genset decides where it can live.
• Plumbing to the tank. Ideally with a diverter so you can taste and test the first minutes of product water before it joins your drinking supply.
• Commissioning. First run, pressure set, water tested, and a TDS baseline written down.

The four questions

1. Does the quote include through-hulls, seacocks and hose, or the unit only? This is where quotes diverge most.
2. What is the cable run, and does my existing bank and breaker suit it? An undersized run drops voltage under load, which shows up as poor output and gets blamed on the membrane.
3. Where exactly will it mount, and can I reach the prefilter and membrane from there? Ask to be shown the location before work starts. An install you cannot service becomes an unserviced install.
4. Is commissioning included, and will you record a TDS baseline at handover? Without a first-day reading you have nothing to compare against when output falls in year three.

What makes an install expensive

Distance and access, mostly. A unit that sits near the sea, near the bank and near the tank is a straightforward day. One that has to live in a forward locker with a cable run past every bulkhead in the boat is not. Joinery that has to come out and go back is labour that has nothing to do with watermakers at all.

Modular systems help here: the pump, the membrane housing and the controls mount separately, so they fit around obstructions a single frame will not clear. That flexibility is often worth more than the specification difference between two units.