This topic always gets me riled up; I'll do my best to keep it cool.
Disclosure: I am an American drinking water treatment and distribution operator.
Why are you buying bottled water? Is it for aesthetics; that is, you have a problem with the taste/odor/color of your tap water? Or are you concerned with your safety? If the latter, look at
http://www.mde.state.md.us/programs/Water/Water_Supply/ConsumerConfidenceReports/Pages/programs/waterprograms/water_supply/ccr_links/baltimore.aspx and find your relevant Consumer Confidence Report. It is rare that you will find a public water system in America that is not producing water that is safe to drink.
Are you buying bottled water so you can have it on the go because you are such a bad-ass athlete that your hydration demands are greater than most other mortals? Look into any number of reusable bottles. They come in all shapes and sizes and materials. Plastic, metal, leather, whatever you want.
I really recommend just sacking up and embracing the taste of tap water--most tap waters are high in mineral content that is good for you. It has different flavor because of the minerals in it that bottled water is lacking. It is also much more heavily regulated and monitored than bottled water which is regulated like other beverages, eg soda. Do you really want to drink something that is produced by and regulated under the same guide lines that soda manufacturers adhere to?
Most Brita and Pur water filters are activated charcoal filters (most often granular activated carbon) that do little in the way of making the water and 'safer'. GAC will remove some biological constituents but, as mandated by federal law and often more greatly enforced by state primacy agencies, there is a disinfectant residual detectable in your drinking water so biological constituents are not really of concern. The carbon filters will do wonders for taste and odor problems. However, be aware that the T&O problems could be YOUR fixtures in your home and not actually a problem with the water coming to your residence.
Charcoal filters will NOT stand the test of time. There is not a filter in production for any use (residential or commercial) that can go without service. Most residential (called point-of-use systems) are throw-away style while commercial filtration systems are either physically cleaned (often a reverse filtration "back-wash" cycle, pressure sluice, air-scrub, or chemical cleaning. Or any combination of some/all of those).
POUs are made to be throw-away and replace because if cleaning regimens were prescribed but performed poorly/incorrectly/too infrequently, the risk of drinking more contaminated water is present. (Basically, a super-saturation or bacteria breeding ground can exist.)
Further, charcoal POUs can't really be regenerated/refreshed--even on a commercial level, carbon is most often a single use treatment that is replaced after so many gallons of throughput or a certain level of fouling.
The chemicals used for cleaning filters are expensive and dangerous--Sulfuric, citric, muriatic, phosphoric acids; bleach, sodium hydroxide. All in commercial strengths.
TL;DR: If you're in America, do the Mustachian thing and drink the tap water.