This is lifted from the SSCA board and is a response to a question on how to adjust a water maker to safely operate in fresh water.
Re: Watermaker in fresh water
by SV THIRD DAY
» Mon Dec 16, 2013 4:50 pm
We tell clients that they can use their sea water water maker in a lake, river, or even to process chlorine free
dock water by simply NOT increasing the PSI to a level that will exceed your fresh water production when running on sea water.
What happens is that without the osmotic pressure of the sea water, ALL of the fresh water will want to pass through the RO Memane if you raise the pressure to 800PSI. This HUGE membrane flux can actually rip the membrane and boom....time for a new membrane.
If you are running at 800PSI typically, then in freshw water you will be running around 150-250PSI to reach your rated output.
Since I mentioned it, let me back fill a little info on running your water maker from the dock water.
In places like Mexico that DO NOT Chlorinate the city water, you can connect the pressurized dock water up to your water maker and fill your tanks with 5-10ppm fresh water all day long. In additinal to being VERY GOOD for the RO Membrane to be flushed, it removed the worry about taking on dock water. As mentioned above the KEY here it so NOT exceed the rated output of your water maker or RO Membane, so NEVER adjust your pressure up to 800PSI while processing dock water, lake water, river water, or brackish water. Let your "Normal" prodction rate be your PSI limitor. If you don't have a flow meter on your product water...well for heavens sake add one! Monitoring TDS along with the flow rate at a set PSI can give you info on the health of your membrane.