In brief
Treat the smallest appropriate part of the plumbing system unless the household objective genuinely requires more.
Point-of-use treatment
An under-sink or tap-level system treats water at one outlet. It can suit a defined drinking-water preference and limits the required flow and cartridge size.
Whole-house treatment
A mains-entry system must support peak household flow and be installed with suitable isolation, bypass and maintenance access. It affects more outlets and increases equipment and servicing requirements.
Questions before choosing
- Which outlets need a different water characteristic?
- What peak flow must the system support?
- What happens if maintenance is overdue?
- Where will drains, replacement access and bypasses go?
- Does the treatment affect boilers, appliances or drinking-water provision?
Whole-house is not inherently better. It is justified only when the intended outcome applies across the property.
Sources and further checks
- GOV.UK: Check the quality of your drinking water
- Water Regulations Approval Scheme: consumer guidance
Sources are provided for verification. Product specifications and local supply information can change, so check the current primary source before acting.