Whole-house equipment treats water near the service entry; an under-sink RO system usually serves a drinking-water faucet. Choose according to the goal and intended fixtures rather than assuming either is a universal solution.
| Question | Whole-house treatment | Under-sink RO |
|---|---|---|
| Where is it used? | At the entry, covering the plumbed scope in the proposal. | At a drinking tap; other connections must be specified. |
| What decides performance? | Media, supported claims, flow and maintenance. | Exact system, supported claims, feed conditions and maintenance. |
| What site details matter? | Main line, space, access and design-specific drain or power. | Cabinet space, faucet, pressure and system-specific connections. |
| What must be verified? | Which fixtures are treated and how operation is checked. | Which taps are supplied and how startup/service is checked. |
One goal may need one system
If the priority is drinking and cooking water, begin with the kitchen's actual needs and compare the supported performance of the proposed RO system or drinking-water filter. Do not assume that a whole-house filter offers the same reduction claims. Equally, an under-sink unit does not establish treatment at showers or laundry fixtures.
Multiple goals need separate explanations
A household may consider entry-point filtration, softening and drinking-water treatment for separate purposes. Ask why each component is proposed, what measurement or goal supports it and whether simpler equipment meets the stated need. The whole-house guide and softener guide explain the separate discussions.
Confirm the source and the ownership plan
Use the local water guide only for the matching City supplier; a private well needs property-specific testing. Compare written installation scope, replacement supplies, service access and warranties using the cost checklist. Neither the illustration nor the name of a technology establishes performance at your property.