My naturpathic doctor and another source always told me to replace the minerals lost due to purifying water. In this age we really do have to purify our water, but that takes out good minerals as well as bad. There are liquid "Trace Minerals" supplements you can get at the health food store. Some of them simply taste salty, some have flavor added such as lemon.
This article explains why restoring electrolytes to purified water is so important.