What's the best undermounted filter? I want to filter the cold water on my kitchen sink.

Alan,

There is a vast range of brands with no 'right' one so I suggest you do your research - use Consumer Reports if you're a member, read the reviews on Amazon, and google 'under sink filter review'. 

I'm not sure what type of filter you are considering.

• What is the water issue you are trying to address?
• Do you need a simple filter system that traps particles and/or chemicals?
• Or a more expensive and larger Reverse Osmosis system that produces more clean and pure water?

For most city water, a 3 stage filter is adequate - prefilter, charcoal filter, and postfilter. You might want to buy an extra set of filters so you have them on hand when it comes time to change them, which is 6 to 12 months, depending on the filter brand, and quality of your water. 

Whatever type or brand of filter system you end up buying, see if you can get a 'premium' faucet as an upgrade instead of the generic plastic one that may come with your kit. I believe it's worth the extra expense.

For more information:

Read "Can you recommend a whole-house water filtration system?" a Q&A answered by Tammy Schwolsky.