Too much water? Too little water? Powdered electrolytes (similar to the liquid Pedialyte I bought yesterday for my husband) to add to water? Potassium, calcium and/or magnesium from foods or pills?
Here is a link to a Mayo Clinic article related to this topic: https://www.mayoclinic.org/diseases-conditions/muscle-cramp/symptoms-causes/syc-20350820
I'm another person who has a tendency to cut back on the liquids due to the lack of easily accessible toilets on tours. I've learned over time that sometimes the inevitably much younger RS tour guides, whether local or general, aren't the best at thinking about this issue. As a result, I've had to make it my own priority, which sometimes means that I have to miss the beginning of something and/or be one of the last people to get on the bus. Thank goodness for the buddy system!
Not so oddly, I've never experienced those kinds of challenges on the parts of my trips that are solo and totally planned and controlled by me. In either case, I have liter bottles of water in my room, one still and one sparkling. On tours I take those on the bus and replace them as needed.
Whether on my own or on tour, I never carry water with me out on the street. I prefer to stop, have a snack and a drink, rest and watch the world go by. Even on tours, this is often possible, although it might happen in a museum or other facility instead of a café.