Tap Water is usually the worst source of water. Watch my detoxification webinar, I give some statistics on the chemicals in tap water.
Filtered Water is better but many chemicals can still pass through the filter.
Reverse osmosis is good but it removes a lot of the good minerals also, so you need to supplement your diet with good minerals.
Distilled Water is only good for short periods of time because it is void of all minerals. You must supplement you diet with good minerals if you drink distilled water.
Spring Water! this is a good source of water. The way nature intended it to be. BUT you need to make sure it is not contaminated by runoff or other harmful chemicals.
How any type of water is processed, stored and the type of container it is put in can also be a source of contamination or leaching.