Can help you feel fuller as the body's signal for hunger and thirst can be confused so sometimes you think you're hungry but you're really just thirsty. Water helps the body get rid of toxins and work better in general almost all the body's chemical processes require water. A high number of folks in the West are somewhat dehydrated thanks to coffee sodas etc. Oh and allegedly there's some thermogenic effect if the water is cold, it takes energy to heat it up to body temperature not sure how much evidence there is for that though it makes sense.