Overview
This guide uses Selection Logic so you can choose by need and evidence. Key traps: RO vs ultrafiltration confusion; TDS pen misuse; wastewater ratio.
Theory anchor: T1 Matching Theorem—good choices match your needs, not "objectively best" configs.
Step 1 → Need clarification (M1)
Use M1 Need Clarification to define real usage and constraints.
Scenario analysis
| Scenario | Primary considerations |
|---|---|
| Drinking & safety | RO, filter grade, certification |
| Hard / high TDS | RO, wastewater ratio, softening |
| Kitchen use | flow rate, dual tap, space |
| Filter cost | filter life, price, compatibility |
Example need list
- Must-have: key metrics for main scenario
- Nice-to-have: experience and convenience
- Bonus: support, brand, expansion
Step 2 → Allocate cognitive budget (T2)
These products are typically medium-to-high value and low reversibility. Use T2 Cognitive Budget and Decision Reversibility to allocate time.
Suggested time: need clarification 30 min; evidence gathering 2–2 h; comparison 1 h.
Step 3 → Multi-dimensional evaluation (M2)
Use M2 Multi-Dimensional Evaluation. In this guide, stress: Stress: RO vs ultrafiltration—different removal and water conditions; TDS pen—only dissolved solids, not full safety; wastewater ratio—weigh cost and environment.
Evaluation dimensions
| Dimension | Sub-items | Evidence sources |
|---|---|---|
| Filtration | RO/ultrafiltration, filter grade, certification | certs, reviews |
| Water quality & flow | flow rate, wastewater ratio, TDS meaning | tests, docs |
| Filter & cost | life, unit price, compatibility | TCO |
| Install & space | under-sink/counter, size, plumbing | specs, install |
Weight example
Per T1, set weights by your needs, e.g. Filtration 35%%; water quality & flow 25%%; filter cost 25%%; install & space 15%%.
Step 4 → Bias & persuasion hazards
- Anchoring effect: don't anchor on high-end prices; fix budget and needs first.
- Confirmation bias: write criteria before browsing; avoid justifying a favorite.
- Halo effect: brand and marketing carry value assumptions—see T1.2.
- Specs and claims: rely on measurements and third-party data; beware claimed vs actual.
Step 5 → Decision + validation (M5)
Apply M5 Decision Validation.
Checklist: core needs met (fit score); within budget; satisficing threshold (T4.2); still satisfied after cooling-off.
Post-purchase: Need consistency—after 1–3 weeks, check real usage vs expectations, key metrics, regret points.