I don't know about water being link to causing allergies but I also know of someone you is allergic to water,
As mentioned chlorine can be harmful, also flouride has been connected to causing bone cancer in boys
http://www.organicconsumers.org/food...ride071505.cfm
Since dogs only drink water, it possibly may explain the rising number of osteo sarcoma deaths. Unfortunately Brita water filters does not remove the flouride but will help to remove chlorine