A flood of costs and a trickle of cash

Andy Pag attempts to rebuild a Spectra watermaker on a budget

Maybe I should have listened to the voice telling me to walk away, but I needed a watermaker after my Osmosea unit died and here was a Spectra unit, supposedly the Rolls Royce of watermakers, being advertised at a fair price.

Whenever the owner of something that's not working tells you how easy it is to fix, ask yourself why they haven't done so themselves. It'd been left in a heap for a few months and who knows how many bits of it had stopped working in the meantime. "You'll probably find it just needs a bit of a clean" the seller chirped as I handed over the cash against my internal screams to turn and walk away.

The thing that sold it though was that I'd read Spectra sell a rebuild kit with all the internal parts that effectively make the unit like new. Later that evening I learned these kits retail at over £1,000, for a handful of proprietary parts and a lot of imperial-sized O-rings - not an option for me. So the challenge began to see how cheaply I could get fresh water out of this thing.

The unit is essentially in four parts: the 12V pump, the pressure intensifier (also known as a Clark Pump), the membrane, and the electronics.

Fresh water can permeate the membrane, which filters out salt, bacteria, and most minerals dissolved in the seawater making it safe to drink, but it needs to be fed with a pressure of 60bar and a flow rate around 9lt/min in order to work. The 12V pump is meaty, it draws up to 20A, but even that isn't enough to get the pressure and flow needed. That's the job of the intensifier. It's a collection of valves and pistons that cleverly recycle the pressure at the output of the membrane and add it to the pressure going in. Over the first couple of minutes of operation the pressure in the intensifier builds up and as it hits 60 bar the unit starts producing clean 'product' water.

The pump