If you're looking for a reverse osmosis alkaline water dispenser, one of the two primary types of home water filtration system, there are a few things you need to know.You may already know that investigators have found some 2100 chemicals in our water, and that while most of them are present in low concentrations, many of them are known to cause cancer, and many of them are suspected to cause cancer, or otherwise be dangerous.Reverse osmosis systems are widely sold in the U.S., but many people install carbon filtration units, which have a number of advantages. We can't deal with all the differences here, but here are a couple of considerations:Reverse Osmosis Water Dispenser SystemsThey function by forcing water through a semi-permeable membrane. The membrane's holes are small enough to filter out most contaminants in the water, and just large enough to let the water molecules through.RO systems do a great job of removing sediment, salt, nitrates, and many other chemicals, cysts and bacteria, however there are a few problems with this approach.A reverse osmosis unit also filters out the calcium, potassium, and magnesium-minerals that the human body needs, and that make the water taste good. Many authorities believe that changing the acid/alkaline balance of the water by removing all the minerals is harmful.On the other hand, one of the things you would want removed from the water has molecules that are smaller than a water molecule, so they slide right on through the membrane. These are called "Volatile Organic Compounds", or VOC's.Breakdown products of oil and gasoline; many pesticides and weed killers; many pharmaceuticals; and many household cleaning products form VOCs-not something we want in our water.For this reason, a good reverse osmosis water dispenser unit for home use must also include carbon filtration, which does capture VOC's. So while it's not accurate to say that an RO unit won't remove VOC's, as some competitors do, it is accurate to point out that it must have an additional carbon filter to do so. In other words, in purchasing a reverse osmosis system, you must be certain not to buy one without a carbon filter.Another issue with reverse osmosis water dispenser systems, no matter how good a job they do at removing contaminants, is that they waste a lot of water. Depending on the system, 3 to 10 gallons of water are wasted for every gallon processed.Solid Block Activated Carbon, ("SBAC") Filtration SystemsAn SBAC system filters contaminants in two ways. Contaminants get trapped in the incredible number of little nooks and crannies and passages in the carbon-a pound of solid block carbon contains over 6,500,000 square feet of surface area. Secondly, through the process of adsorption, foreign substances are attracted to and held by the carbon.Of course a good multi-stage SBAC system filters out sediment, chlorine, most cysts and bacteria, and most everything else, along with the VOCs. It doesn't waste water, and it's typically less expensive to purchase.An SBAC unit also has an operating cost advantage over a reverse osmosis water dispenser. The SBAC unit I installed to protect my family has an operating cost of less than $.10 per gallon. The typical RO unit has an operating cost of about $.25-$.35 per gallon.So... while better reverse osmosis water dispenser systems generally do an acceptable job, for my money, the activated carbon system is usually the better choice.