Exclusively breastfed babies do not require additional water even when it is very hot outside, as long as baby is allowed to nurse as needed. Even in extremely hot, dry weather your baby can get all the liquids needed via breastmilk.
Smooth muscles contract very slowly, whereas skeletal muscles can contract at different rates. Skeletal muscles can be composed of fast-contracting fibers, slow-contracting fibers or a mixture of both.
The skeletal system is different from the smooth muscle system in organs like your liver and the cardiac muscle in your heart because the skeletal muscles contract voluntarily.