What does it cost to install a reverse osmosis watermaker on a boat?

For a 35 to 45ft cruising boat, budget £7,000 to £13,000 for a small reverse osmosis watermaker professionally installed, rising to £12,000 to £20,000 or more for higher output, automation or difficult access. Check daily water use and available electrical power first: these determine the machine you need and whether installation calls for expensive charging or battery upgrades.

Equipment and installation costs

These are UK planning allowances including VAT, not fixed quotations. Imported equipment, exchange rates and local yard charges affect the final bill.

• Compact 25 to 40 litre/hour equipment: approximately £4,500 to £7,500, with straightforward professional installation bringing the total to around £7,000 to £11,000.
• Mid-sized 50 to 80 litre/hour equipment: approximately £6,000 to £10,000, typically £9,000 to £14,000 installed.
• Larger or highly automated systems: allow £12,000 to £20,000 installed. Larger yacht installations can cost well above that.

Schenker, Spectra, Rainman and Dessalator are useful brands to compare. Check output, power consumption and included accessories alongside price. Installation costs can differ considerably between a portable package and a permanently plumbed system.

For a straightforward yacht installation, allow roughly £1,500 to £3,500 for labour and £500 to £1,500 for plumbing, wiring, mounting materials and fittings. Check whether the installed price already includes these items before adding them again.

Match output to demand

Measure consumption over several normal cruising days. Two people using 40 to 60 litres daily can usually manage with a 30 litre/hour machine running for about two hours. Four people using showers freely may justify 60 litres/hour or more.

Figures from representative efficient systems show how electrical demand varies:

• 30 litres/hour: around 110W, approximately 9A at nominal 12V, and roughly 22 to 26kg depending on configuration.
• 60 litres/hour: around 240W, approximately 20A at 12V, and about 31kg.
• 100 litres/hour: an efficient system may use around 400W and weigh about 53kg.

These figures apply to particular efficient designs, not every watermaker. Conventional high-pressure pump systems can draw substantially more power. A 240W machine running for two hours consumes approximately 480Wh, or 40Ah at nominal 12V, before associated loads and losses.

Cold seawater and changing salinity affect production. Leave a margin when choosing capacity rather than relying on the advertised maximum, and check the manufacturer's rated test conditions.

Installation extras

First, check for a suitable seawater intake, a dry mounting position and access for servicing. A compact pump assembly may fit easily, but its membrane vessel still needs a long, accessible locker.