Hi Bill and All:  

Perhaps I can add something about the behavior or the TDS (electrical conductivity = EC really) of the product water upon startup. 
Background:  My system is the original Amel system for a vintage 2001 (hull #335 SM).  It had (and still have) the sham TDS circuit board installation from Dessalator.  I have however re-fitted my system with an external continuous monitoring EC sensor on the product water line along with manual bypass valve switch and LED indicator light as well as a 110 decibel sonalert to alarm if the TDS (EC) rises above the level I select on the TDS sensor.   I have also installed a 7 day timer that flushes my system with product water from the tanks for 5 minutes every other day (uses about 4 liters of water per flush cycle) while I am not on the boat.  Haven't used sterilizing solution in more than 10 years now and have avoided all the corrosion problems associated therewith.  Additionally I am on only my 3rd set of membranes in 18 years. Those boats refitted with the Dessalator automatic flushing board and 54s etc I presume have a TDS sensor that actually works.

On my boat the Startup TDS readings:   Remember this is with the system completely filled with fresh water and the pressure knob turned anti-clockwise:   Upon initial startup the TDS is low (somewhere in the vicinity of where it was when the system was shut down, and in my case electrical conductivity (EC) of approx. 450 micro-siemens, 1 micro-siemen = .0055 PPM TDS, so this is about TDS of 2.48 ).  After a few seconds of raising the pressure to the operational range by turning the knob on the control panel to restrict flow and thereby increase the membrane side pressure, the EC (TDS) rises almost immediately to max out my salinity sensor over 5,000 micro-siemens.  About 20 seconds later, the conductivity/salinity begins to fall back to the acceptable range.  When it falls to this level I manually throw the switch to activate the diverter valve (valve is normally closed / in diversion) and simultaneously arm the sonalert alarm system.  The EC spike that occurs upon start-up has always baffled me as it occurs no matter how many months the system has been flushed with fresh water.  I can only assume it is due to some residual salts in the nooks and crannies of the membranes that is briefly excreted with the first product water.  These findings are consistent and is perhaps the basis of the 1 minute bypass timer in the  automatic system that Dessalator engineered.  I really like my manual system and I love that the system continuously monitors and instantaneously alarms if there is high TDS (EC). 

Just some food for thought on my experience with independent monitoring of the EC (TDS) of the Dessalator water maker.

Sincerely, 

Gary S. Silver
s/v Liahona
Amel SM 2000 #335
Puerto Del Rey Marina - Puerto Rico

Sincerely, 

 I have th