I know a lot of people that only drink 3 or 4 cups of coffee or tea and don't drink anything else for the day, i often wonder how many people out there are in a dehydrated state and what this does to our nerves over long periods.
Water is so necessary for survival, an average adult is made up of 60 -70% water, we can go without food for almost two months, but without water only a few days, every cell and every system in our bodies depends on water.

I have read that without water we'd be poisoned to death by our own waste products when your kidneys remove uric acid and urea, these must be dissolved in water. if there isn't enough water, wastes are not removed as effectively and may build up as kidney stones, water also is vital for chemical reactions in digestion and metabolism. It carries nutrients and oxygen to the cells through the blood and helps to cool the body through perspiration., also without enough water you could end up with excess body fat, poor muscle tone, digestive complications, muscle soreness, fatigue and headaches, water regulates our body temperature, flushes toxins out of your body and is essential for healthy skin, provides a moist environment for ear, nose and throat tissues.

You can easily get sick of plain water, add a bit of lemon or lime for a touch of flavor, water filters aren’t very expensive but do a pretty good job,, or by simply boiling the water first can change the taste of it.

The water needs are not the same for everyone, depends on the individual, where they live, exercise etc, the link below has a good explanation.

http://www.mayoclinic.com/health/water/NU00283