Friday, March 8, 2013

How to Drink Seawater

Between re-hydrating the freeze dried food and keeping my body hydrated, I anticipate needing around 6 liters of water per day. Throw in a little water for non-consumption purposes and a solid safety margin and we're talking approximately 500 pounds of water on board for the race which will substantially slow down a little boat like Jeroboam.

Katadyn PowerSurvivor 40E installed under the galley sink
It was time to suck it up and get a reverse osmosis desalinator which turns the ocean's salt water into potable water. The smallest, lightest one I found is the Katadyn PowerSurvivor 40E which weighs in at a very reasonable 25 pounds and produces my daily requirement of 6 liters in about 2 hours. Other boaters with greater water requirements than I are ga-ga for Spectra units but they're considerably more expensive so this was the best option for me.

Installation was challenging primarily because I have some particular needs and zero plumbing experience. In a nutshell:
Raw water filer & 30 micro pre-filter,
also under the galley sink

  • Add small, 3 gallon water tank for desalinator so output is segregated from main tank
  • Plumb desalinator tank w/ valve to large aft water tank
  • Plumb desalinator output to dedicated sink faucet for testing prior to sending to desalinator tank
  • Plumb seawater from thru-hull w/ scoop strainer to raw water strainer to 30 micron pre-filter to desalinator w/ options to instead run desalinated water through (for cleaning) or membrane preservative (for storage)
  • Plumb desalinator tank and large aft tank to galley foot pump w/ option to draw from either

Dedicated tank for desalinator
product water in cabinet below icebox
Lots of pieces to this puzzle were required, thankfully there are places like McMaster-Carr out there with just about any bit of hardware you could possibly imagine. I once read someone's post on one of the sailing boards claiming he could construct his own space shuttle from the many parts sold here and I don't doubt him. But still, it was trial and error for several weeks as I pieced it all together.

I had my first successful test last night around 3 AM when the tide was coming in and made about 5 liters of perfectly delicious fresh water from disgusting salty seawater. Amazing.

The reverse osmosis technology behind it is fascinating but I won't go into it here.


  1. Jonny - what do estimate your daily energy requirements to be to run the desalinator?

    1. The unit's specs indicate 4 amps/hour but I'm observing closer to 5 in practice so if I run it 2.25 hours/day (0.25 hours for cycling the pump & getting clean water flowing + 2 hours to make 6 liters), I'll burn about 11.25 amps.