DO NOT buy a water alkalizer/Ionizer. These bogus products are artificially Ionized via electrolysis, a process found nowhere in nature that has known damaging effects on the bodies energy system. These filters also have adverse effects on the digestive system due to the unnaturally high PH balance and contrary to health claims they do not alkalise the body.
While Reverse Osmosis is safe, the process which removes harmful contaminants like flouride also removes trace minerals.
By far the best system is the innovative "Wellness water" purifier. Wellness water systems first filter out unwanted contaminants and then the water passes through an array of ceramic magnets surrounded with magnetite, the same iron rich rock found at the world's great springs including that of the famous hunza tribe, and the water's hydrogen bonding network is altered and its bonds realign to create a water that is more soluble "wetter water". It is then past through Tenko seki far infrared rays (known for their powerful healing and detoxifying effects) which naturally ionizes the water (as opposed to the dangerous process of electrolysis). The resulting effect is a more soluble water with a shortened cluster cell (like the water in our bodies cells) that is active at the cellular level.
Check out their website at http://www.wellnessfilter.com/ and be sure to check the comparisons link for an explanation on why you should never drink from water alkalizer/ionizer filters....