The path
Where the water comes in
Everything starts at the main line. What you fix there, you fix for every tap and every shower in the house.
One
The softener
Resin trades the calcium and magnesium out before the water reaches the heater and the fixtures. Scale stops.
Two
Carbon at the main line
One filter where the water enters takes sediment, chlorine and chloramine out of every tap and shower in the house.
Three
Reverse osmosis at the sink
Pre-filters, a membrane and a small tank with its own faucet. Drinking water down to a few parts per million.
Four
Then we keep it running
Media lasts years, filters do not. We track the change so you do not have to.
The point
Water you stop thinking about
Which of those three a house needs depends on what is in the water. The test at your kitchen tap says which.