Not only is bottled water potentially bad for you (with its hidden dangers of BPA and other estrogen mimicking plastics), and bad for the environment (due to its massive use of fossil fuels to move the water across the planet's surface, the polluting effects of the plastic after it is discarded, etc.), but it costs an arm and a leg also. Using a water filter to get fresh water is extremely cheap in the long run; in fact, the device usually pays for itself within a few weeks.
The initial purchase price of a water filter is the main cost of obtaining clean, high quality water through this means. A good water filter can cost anywhere from a few tens to a hundred or so dollars, depending on its size, capacity, and construction.
The filter case, tubing, spigots (if present), and other features typically last for years, since they are not subjected to a lot of stress. They will wear out eventually, but if treated carefully should endure well beyond the manufacturer's limited warranty date. When considered from this perspective, the filter itself will end up costing only a few cents a day, or week, when its initial purchase price is divided up over the full lifespan of the item.
The internal cartridges, which do the actual “heavy lifting” of filtration, need to be replaced more frequently – every three months, six months, yearly, and so on, depending on their design. This does represent something of an ongoing expense, but it is still far cheaper than buying bottled water continually on a daily or weekly basis.
Using water filters saves you money in other, less immediately visible ways, too. You will generate a lot less garbage, lessening the amount of time you need to spend sorting out recyclables and also cutting down on the size of your garbage pickups. Bottled water is heavy, so it increases your car's fuel consumption somewhat when you are bringing large or numerous bottles home on a regular basis. You may need to make many less trips to the store if you aren't using bottled water, too.
Though this is far too abstract to be properly measured, having access to clean, fresh, safe water to drink may ultimately save you a lot of money on medical bills. Unfiltered or bottled water may cause subtle problems over time, degrading your health and making you more likely to suffer from various ailments.
Eliminating the risk of immediate hospital bills from illnesses inflicted by unfiltered water – such as diarrhea or vomiting – is another way that water filters can save you money in the short run, particularly while traveling in areas where water quality is shaky at best.