Chosen Solution
These filters don’t actually get rid of hard water. Are for chlorine and sediment and help with the taste and smell. You will need a water softener. You may have one for the house already but not all of the water is softened depending on how it’s hooked up. Most outside hose faucets aren’t connected to the water softener. And if you have a water softening system it sounds like the water line to the fridge is not connected to that system.
The refrigerator water filter is trying to remove some dust, contamination, and possibly chemicals. So if your tap water is having low contamination then filter won’t improve the PPM level. We live in Austin, TX where tap water has 165 ppm level. With refrigerator filter it is coming to 155 ppm. However, if you use RO filter (under the sink), it would be using Reverse Osmosis (RO) process to remove above contamination as well as (some good) minerals. Since your PPM is high, the tap water is hardened with lot of minerals (many of them are good) and when it goes through RO, it remove all these minerals and giving you low ppm count. You would be OK to use tap water itself. Refrigerator filter isn’t adding much new value for you — IMHO.
