Guides · Buying
Whole-House vs Under-Sink Filters
Point-of-entry treats every gallon; point-of-use treats the glass. How to decide, and the order to install them in when you need both.
The dividing question
Whole-house (point-of-entry) treatment sits on the main line and treats every gallon: showers, laundry, toilets, garden taps. Under-sink (point-of-use) treatment serves one tap and treats only what you drink and cook with.
Ask what the contaminant affects. Sediment, iron, and hardness affect plumbing and appliances across the house. Lead, nitrate, arsenic, and PFAS are drinking-water concerns at the glass.
When whole-house makes sense
Heavy sediment or rust from a well: a whole-house sediment filter protects every fixture and the water heater.
Hardness: a softener at the point of entry is the only practical fix, because scale forms wherever water is heated.
Iron, manganese, or sulphur odour: point-of-entry treatment keeps the problem out of the shower and the laundry, where it is most noticeable.
What it does not solve cheaply: lead from your own plumbing, nitrate, or PFAS at low levels. Those are more economical at the tap.
When under-sink makes sense
A health-based contaminant in the CCR or a well panel: lead, nitrate, arsenic, PFAS, or cysts. Treating the drinking tap costs a fraction of treating the whole house.
Taste and odour only: a carbon under-sink or even a faucet-mount filter is usually enough. Whole-house carbon for a taste complaint is expensive overkill.
When you rent or cannot touch the main line: under-sink or countertop keeps the decision reversible.
Installing both, in the right order
Order on the main line: sediment pre-filter first, then any iron/sulphur treatment, then the softener if you use one.
Then treat the drinking tap separately. Putting a fine carbon block before the softener shortens its life, because it takes the sediment load the pre-filter was there to catch.
Keep a bypass valve around each whole-house stage so you can service one without shutting water off to the house.
Cost and maintenance realities
Whole-house cartridges cost more per change and are changed less often; the annual figure depends heavily on sediment load. Budget for two or three changes a year on a well.
Under-sink systems are cheaper to own but only fix one tap. If you fill pitchers and water bottles in the kitchen, that is usually all you need.
Whichever you choose, write the model numbers down. Reordering the wrong cartridge is the most common and most avoidable expense in this category.
FAQ
Quick answers
+Does a whole-house filter remove lead?
Only if it carries a certification naming lead, and it will be an expensive way to solve a problem that usually comes from your own plumbing. Point-of-use filtration at the kitchen tap is normally the better answer.
+Will an under-sink filter soften my water?
No. Softening is ion exchange at whole-house scale. RO reduces hardness at the tap as a side effect, but it does not protect your water heater or shower.
+Can I install a whole-house filter myself?
If you are comfortable cutting into the main line and can isolate it, yes. If not, this is the one job in the category worth paying a plumber for, because a leak there floods the house.