Water hydrates your body when it enters it. It nourishes your cells and muscles. Too much water, meaning extreme amounts of water intake, however, could cause over dilution in your body, and possibly cause your cells to burst. Otherwise, drinking a normal amount of water daily is healthy for your body."You need water to: 
•Digest food, dissolving nutrients so that they can pass through the intestinal cell walls into your bloodstream, and move food along through your intestinal tract. 
•Carry waste products out of your body. 
•Provide a medium in which biochemical reactions such as metabolism (digesting food, producing energy, and building tissue) occur. 
•Send electrical messages between cells so that your muscles can move, your eyes can see, your brain can think, and so on. 
•Regulate body temperature — cooling your body with moisture (perspiration) that evaporates on your skin. 
•Lubricate your moving parts

If water is contaminated with something else that is bad for you then it can be bad. Also it is possible to drink too much water. Most people don't get enough water. We should not wait until we are thirsty to drink. But some go way too far and drink too much and this results in" Water Intoxication (also known as hyper-hydration or water poisoning) this is a potentially fatal disturbance in brain functions that results when the normal balance of electrolytes in the body is pushed outside of safe limits by over-consumption of water.
hope it helps u...
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