US, tap water is perfectly good to drink.

Having visited Iceland a few years ago, Iceland’s tap water is the best tasting water I’ve ever had anywhere. Please take this opportunity to try it while you’re there.

Not an immediate remedy, but my input here is not to mistake rest for healing.If your back pain is muscle related, rest may relieve the pain, but will also continue to allow those muscles to atrophy, potentially seeing you up for more pain. Active recovery, building back the strength of those muscles, can be very important if this is the cause of your pain.

In the end, a doctor of some sort will be your best bet for finding out the root cause of your pain, and generally the appropriate way to address it.