We should all drink more good clean water everyday to hydrate and cleanse our bodies. The absolute minimum is half our bodyweight in ounces, i.e. If you weigh 160lb, you need to drink 'at least' 80 ounces of water. Ideally you should add an alkaline based 'green drink' to the water, something like wheatgrass powder. Wheatgrass helps your body to become more alkaline than acidic. When your body's acidic, this is when you get ill, feel dreadful and your red 'oxygen carrying' blood cells won't move through the body effectively, making you feel tired and sluggish.
The utlimate gift you can give your body is this superhyrdation process with green drinks. If you did this for just half a day, I guarantee by early afternoon you'd be feeling great! Go on, try it!