I find not staying hydrated affects my concentration, gives me headaches, and affects my strength.
Water is pretty important, you only last a day or two without it.
Our ancestors built their villages & camps almost exclusively around good water sources, even though they represented danger due to flooding. We still do to the modern day. Losing that water source through drought or contamination would doom a community.
Going back thousands of years they would make water containers from animal hides, gourds, clay and whatever they could invent to carry water with them, because they didn't know where they would find potable water.