Question:
While cruising on Lake Superior, we pump lake water into our freshwatertanks and have always added 1 Tbsp of household chlorine per 10 gallonsto kill any of the bad critters. I then add an equal amount of vanillaextract (real or fake) to kill any chlorine taste. This has worked forme for years with no ill effects.

I now find that chlorine supposedly doesn't kill the giardia cysts, andthat one must use 4 drops per liter of 2% iodine to do this, dependingupon the water temperature and the concentration of the bugs. This worksout to about 1 Tbsp per 10 gallons, a drop being .05 ml. I also find outthat one can kill the iodine taste with either vitamin C or lemon orlime juice, but that you have to wait 30 minutes or so for the iodine towork, as these "taste modifiers" kill the action of the iodine. Not sowith the vanilla, I'm told.

Could I mix the vanilla, chlorine and iodine in advance as a"purification tail" and add three Tbsp per 10 gallons to my tank?

Answer: Giardia (and Crytosporidium - a much much worse protozoan than Giardia)is effectively removed by filtration with an absolute (100%) rated 1.0micrometer (µM) filter. This infers a 'certified' 100% retention at 1µMand is not something you can buy in a hardware store!!! Important -"certified" 1µM (100% retention). Plus you need the technicalknowledge to be able to 'technically' change and sanitize the filter andits housing without contaminating the system. Cryptosporidium is a*common* pathogen found in Great Lakes water .... and universally ispresent in most worldwide municipal water supplies that have 'surfacewater' as their source. (Do websearch for: Milwaukee + cryptosporidium)

The efficacy of using Iodine is dependent on the consumption of iodinewith the system components (chemical reaction with the tankage) ...variable and unmeasurable for "boat people".For other bioburden "maintenance", Chlorine is added to a concentrationof 1 part per million - add just enough Chlorox, etc. to the water sothat you can "just *BARELY* perceive the smell of the Chlorine" in theoutlet water.

To kill the 'taste', filter at (as as close as possible to) the spiggotwith a carbon packed filter. If your water tastes bad, mechanicallyclean the tank to remove dead bacteria, bacterial scum, etc. ...consider to change the vent lines and ALL piping if grossly discoloredwith mold intrusion. (Suggest that you add a hydrophobic 0,2µM filter onthe tank air VENT .... or wrap/tape the vent outlet with a BIG wad ofsterile gauze, keep it DRY, and change seasonally).

Leave the vanilla and lime juice for mixed drinks, as adding nutrientsto the tankage will accelerate microbial growth.

I personally carry onboard all drinking water, only secured from a SAFEsource. (I usually dont drink water from a 'municipal' source, unlessthe source is well water.)