I routinely use distilled water for brewing and it works great. The water in Madison is pretty hard, and I try to cut back on that.
It doesn't hurt that I like the softer hop character that comes from using softer water.
As for the original question, I'm pretty sure you'll be fine. According to Wikipedia, iodized salt is produced by mixing 2 ounces of potassium iodate with 1 ton of sodium chloride. And since of those two ounces, not all of it is iodine. Potassium iodate is KIO3, so
K: 39.0983 g/mol
I: 126.90447 g/mol
O: 15.9994 g/mol x 3 = 47.9982 g/mol
total = 214.00097 g/mol
percent iodine by weight in KIO3 = (126.90447/214.00097) * 100 = 59.3008854%
Amount of iodine added/ton = 2 ounces * .593008854 * (28.3495231 g/ounce) = 33.6230364 g
Percent of iodine in iodized salt = 33.6230364 g/[(1 ton * 907184.74 g/ton)+(2 ounces * 28.3495231 g/ounce)] * 100 = 0.0037060737%
Sea salt has an approximate density of 2.2 g/cm3 (source:
WikiAnswers - What is the density of sea salt).
This means that your 1/2 teaspoon weighs approximately...
1/2 teaspoon * (4.92892159 mL/teaspoon) * 2.2 g/mL = 5.42181375 g
Of which, only
5.42181375 g * 0.0037060737% iodine = 0.000200936414 g ≈
0.2 mg iodine
That amount of iodine is so small that I couldn't even measure it out on the most sensitive balance in my laboratory (our micro balances are accurate to 1 mg, which is still an impossibly small amount of anything).
