The amount [of iodine] needed to purify a day's water corresponds reasonably closely with the amount I need a day, so it works well.
I have just read back my post and this one part was inaccurate, sorry about that.
I meant to say that the amount needed to purify a day's water is within the tolerable limits, but it is actually much more at the higher end of what's tolerable rather than the lower end of what's tolerable (as implied by "need").
To purify unsafe water, you need about 1000 micrograms/Litre by my estimation. Primary source from memory was I think:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1638306/pdf/envhper00309-0035.pdf Even then, you should leave it some hours to kill viruses/cysts in addition to bacteria. I leave it overnight.
The 1000 micrograms per litre as an amount to purify its itself debatable also, but going by that figure you would of course get 1000 micrograms of iodine from 1 litre of purified water and 1000 micrograms is already the maximum reccomended amount. (The minimum is 150 micrograms.)
If you drank tap water all day with 1000 microgram/L as your only beverage, you would go several times over the reccomended amount. However, given what I read about scientific studies on populations that have gone over that amount - notably the Japanese - the 1000 micrograms per day upper limit is likely very conservative.
So I drink 1-3 litres of purified water on most days and supplement with mineral water, boiled water, or other drinks above that amount. I am not going to drink tap water with iodine for close to 100% of what I drink. I also sometimes go for some days without drinking it at all.
So just to clarify, if your tap water is perfectly drinkable - e.g. if you live in North America or Western Europe - then you certainly don't need to add iodine to ALL your drinking water at 1000mcg/L purely to meet your iodine needs. You could add it at that concentration to just one glass or water to get above the minimum, or reduce the concentration by a factor of ten if you were adding it to all drinkable water.
Also, to add further, I hope no-one just reads what I've wrote and decides to just go ahead with it. I suggest you either a) don't use this approach to meet iodine needs b) verify this strategy and dosage levels with a relevant professional or c) go back and read the original research and verify yourself. After all, I may have made a mistake. I may be saying something wrong. It is just forum talk. It's not like I have any relevant professional knowledge.
If you are going to go buying bottles of iodine and start making your own calculations, and pouring it into drinking water, which is what I am doing, there are risks. You better know what you are doing. If you put milligrams instead of micrograms for example you are going to drink 1000 times too much and give yourself very serious iodine poisoning.
Also anyone with thyroid conditions, pregnancy possibility, or specific dietary conditions probably should just especially completely ignore all of this advice and see a professional.
Sorry for going on at too much length about this, but after the first post I made I think it was necessary to add this just in case.
mcg = micrograms