You’re absolutely right about that. If you’re perspiring a lot, you should probably also be taking in some additional electrolytes (Gatorade, or similar — just as needed). Under normal conditions, most people’s kidneys regulate the electrolytes quite well. When you perspire, the electrolytes are expelled, rather than being recycled (if needed). You can easily become electrolyte deficient.
Your body will let you know if you need the supplementary electrolytes. I find that “sports drinks” (Gatorade, etc.) taste like the elixir of life, when I need the electrolytes. If I have enough electrolytes, they taste like the cloying salt-and-sugar-water concoctions they are.
Additional info - sometimes not even the water will save you from horrendous leg cramps (usually at night or when lying down) - like screaming so loud the neighbors are thinking of calling the cops or an ambulance - what happens is lactic acid settles in the mussels and needs to be displaced. Drink some brine (pickle juice) when you can get to it or have some one bring it to you - then drink as much water as you can hold.