Water is the most abundant molecule found in living organisms. most mammals, in fact, are approximately 70% water by weight. about two-thirds of this water is present inside cells. the other one-third is present outside cells (e. g., in blood plasma or other body fluids). why is water so important to cells? . a. water determines which proteins are translated from the cellular dna.. b. water is stored in the cells to be used when the organism gets thirsty.. c. almost all the chemical reactions in life processes occur in solutions with water.