The Katadyn Exstream Purifier is a true water purifier from a biological point of view. It is effective against parasites, bacteria and viruses. You would need an additional carbon filter to remove some of the organic chemical compounds.
I use one all of the time during my trips to Ecuador, as it is easy to carry, fill and use. I generally do not worry about chemical contaminates, but if that were a concern, I have an additional filtering device with an activated charcoal component.
Pete