The best under sink water filter I have found is manufactured by Crystal Quest, a company that has provided high-quality water filtration for residential and commercial use for over 30 years.
They also have an A+ BBB rating and I am continually impressed by their advanced filtration technologies and customer service.
What sets Crystal Quest apart in the under-sink water filter category is the degree of filtration and certifications for their products, as well as their competitive prices.
In addition, every water system they sell is highly customizable to specific filtration needs in any home or business.
The Crystal Quest under sink water filters remove hundreds of contaminants and harsh elements from your drinking water.
They are designed to fit under a kitchen or bathroom sink. These systems attach to your water pipe. A separate faucet (included) is usually installed on your sink or countertop unless you already have an existing one.
All of the CQ under sink water filters are available in a single, double, or triple filter casing system, depending on the degree of filtration you want and whether you need a specialized filter media.
Even the most basic Crystal Quest under sink water filter that has a single filter cartridge uses a multi-stage filtration process, which is highly effective. More cartridges will obviously take up more under-sink space and thus you will want to consider that when choosing a system.
All CQ under sink water filters are BPA-free, made of white Polypropylene. All systems are easy to install and come with everything needed for installation.
The Crystal Quest SMART filtration cartridges use multi-stages of filtration which provides for the removal of many types of contaminants with just this one cartridge.
With this system, water flows through a bed of media made of a special high-purity alloy blend of two dissimilar metals - copper and zinc. This media is a major advancement in water filtration technology that works on electrochemical and spontaneous-oxidation-reduction (Eagle Redox Alloy®) principles. Chlorine is instantaneously oxidized.
Another filtration component is a coconut shell granulated activated carbon (Arsenic Free GAC™). The GAC is an effective adsorbent universally known for removing an array or organic contaminants from drinking water. All Crystal Quest® GAC is a mixed blend of coconut shell and catalytic GAC to address both chlorine, chloramines and their byproducts.
You water will also pass through ion exchange resins, reducing water hardness as well as heavy metals such as copper, lead and aluminum.
This basic under sink system provides 10,000 gallons of water (1-3 years depending on your usage) before needing to replace the cartridge.
The Crystal Quest SMART filtration cartridge is usually more than sufficient for most people, which is one reason I believe these are the best under sink water filters.
However, Crystal Quest always provides many additional water filtration solutions such as Alkalinity enhancement, Fluoride removal, Arsenic removal, Lead removal, and Nitrate removal.
For more information, check out the Crystal Quest page for their specialty under sink water filters.