Used Ispring RCC7AK reverse osmosis under counter water filter. Includes tank, tubing, various fittings, and new spout. This filter system is highly rated and is about $249 on sale new. For more information go to ispring website. A one year supply of filters runs about a $58 at Amazon. The 4 smaller filters change about every 3yrs and the 3 larger filters I change yearly and that worked good for our water in Bismarck.
The system works so well filtering it needs to add good minerals back in.