During municipal water treatment, chlorine and other chemicals are added to the water to disinfect it and keep it from picking up germs in transit. Whilst these chemicals are crucial for keeping your water clean, they’re essentially the wrapping - they protect the product on its journey from the supplier to the customer. But when you get your shopping home, do you eat the packaging?
Water is heavy stuff and carting it about in bottles makes little sense from an environmental standpoint. A far better solution is to filter water at the point of use, after it has already been transported by water main. This method of obtaining clean, chlorine-free water is more cost efficient than a filter jug and is far more environmentally friendly than bottled water.
Municipal mains water can contain small amounts of agricultural herbicides and pesticides. Though the quantities involved are very small, no research has been done into long term exposure to these sorts of chemicals. Certain water filtration systems are sometimes recommended by GPs to people suffering from extreme allergies.