Some of the problems with the water issue could just be the build up of the minerals in the soil if growing in pots like 5 gallon pails from the problem of lack of proper drainage. And that goes for plants in ground as well.
Over a period of time one just normally waters plants till they think that's enough and the soil is wet enough, in a sense. Here sometimes that water's minerals will just build up after awhile in the soil.
With proper drainage one can water the soil in the pot till you can actually see the water flow out the drain holes and thus making the soil evenly wet.. Also, a good flushing of the pail with water atleast once a month will rid the soil of most of these bulit up minerals
This year when I started to use 5 gallon pails I notice in a few of my pots that the soil on top was dry but as soon as I started watering the water built up on the top. That pail was full of water. Here I figured out even with the drain holes I had, though not enough, that just setting the pail on the ground eventuallu blocked the drain holes. So needed to prop the pails up on blocks to get better drainage. That and a few more holes. Worked fine after.
Like some said if you can drink it should be ok for plants. I'd say improper drainage would be a proplem even with some waters that are high in some minerals..
ok I'm done.
make any sense