As it's forced through the kidney, it takes away excess sodium. The overweight person needs more water than the thin one. Larger people have larger metabolic loads. Since we know that water is the key to fat metabolism, it follows that the overweight person needs more water. Water helps to maintain proper muscle tone by giving muscles their natural ability to contract and by preventing dehydration.
Water helps rid the body of waste.
Again adequate water helps flush out the waste. Water can even help constipation. When the body gets too little water, it siphons what it needs from internal sources. The colon is one primary source. But, when a person drinks enough water, normal bowel function usually returns.