Short answer
They solve different problems. A softener removes hardness to protect plumbing and appliances. Reverse osmosis purifies drinking water at one tap. A whole-house carbon filter improves taste and chlorine at every tap. Many Valley homes use a softener plus RO, and add a carbon filter if chlorine taste bothers them.
Water softener
Swaps calcium and magnesium for sodium or potassium through ion exchange, for all the water in the house.
- Protects water heaters, fixtures and appliances
- Ends most spotting and crust
- Doesn't improve taste or remove chlorine
Reverse osmosis
Pushes water through a fine membrane at the kitchen sink.
- Greatly reduces dissolved solids and many contaminants
- Makes great-tasting drinking and ice water
- Only treats one tap, and the membrane lasts longer with softened water
Whole-house carbon filter
Uses activated carbon media at the main line.
- Reduces chlorine, taste and odor everywhere
- Catalytic carbon handles chloramine
- Doesn't remove hardness
Putting it together
For most Valley homes the order is filter (optional), then softener, then RO at the kitchen. Keep irrigation and hose bibs on hard water so softened water doesn't add sodium to the soil.
When to call a plumber
- You're installing more than one system and need them plumbed in the right order.
- There's no softener loop and one has to be added at the main line.
What the plumber does: see water softener installation.
Common questions
Can I drink softened water?
Most people can. It contains a small amount of added sodium. People on sodium-restricted diets often drink RO water or use potassium in the softener.
Editorial note: this guide is general information for Phoenix-area homeowners, not a diagnosis. Conditions vary by home, so a licensed plumber should confirm the cause before any repair.