As we all know that water makes up more than 90% of the word landmass, It is the medium in which the absorption and transportation of solid materials in plants take place.

In humans, its the transportation of food in the body is through body fluid and more than 60% body fluid is water.
Water provides water pressure which helps to maintain firmness that gives support to human tissues.
Water has a fairly high heat conductivity hence heat is distributed evenly all over the body of a living organism.
When Water evapourates from our body either as transpiration or sweats, its brings back a cooling effect
Water is needed for the excretion of waste products from the body
Water is mandatory for the digestion of food

Source: http://www.certaintips.com/2017/02/reasons-why-water-is-important-for-you.html