What has worked the best for her, when she remembers to do it, is to take water from home. We have a well with mineral rich, but not 'hard' water. Your home water no matter the source usually has these. Cola has several of these in their formulas. Water that has been filtered loses most of these minerals.
Most bottled water is filtered so check the label.
It has been in the medical news that many women that drink filtered water have a greater incidence of osteoporosis. Stay hydrated do not wait to be thirsty, thirst is actually a physical panic response. Also the sweeteners in soft drinks bind up the water not allowing the proper exchange of fluids throughout the body. Many times when people feel thirsty due to not enough salt. A simple test is to put some salt on your palm and taste it.