[C320-list] Fresh water tank treatment

[SARA SCHROEDER]

The caps on both fresh water tanks needed to be resealed - again.  I bought new o-rings and wrapped a crap-ton of plumbers tape on the threads.  I got the aft tank sealed and started to work on the forward tank.  I have not used/circulated the water in the forward tank much the past few months.  When I removed the cap I looked inside the tank to find a nice layer of mold/algae/green gunk laying in the bottom of the tank.  I put the nozzle on the hose and hard sprayed the inside of the tank stirring up the gunk.  YUCK!  It's a good thing I only drink bottled water on the boat.  After four fills and dumps the water was "almost" free of any green stuff.  
 
Question - is there a treatment we can put in these plastic water tanks which purifies the water so if I drink it I don't make myself sick?
 
Sara
Wandering Star
Seattle
#707/2000