> Bottled water tends to have sodium in it, even though it is not listed.

Naturally occurring sodium won't make you thirsty.

Bottled water is usually:
1. "spring" (or well) water (disinfected with ozone)
2. municipal water treated by reverse osmosis
3. distilled

# 1 should have naturally occurring sodium (abbreviated "Na").
#2 and #3 have had minerals such as sodium removed (sometimes they may be
added back in)

Sodium can become an issue with water softeners.  They exchange sodium for
calcium/magnesium, thus increasing the sodium content of the water.  People
with high blood pressure are sometimes advised to restrict sodium.

Rob