| Applicable standard | NSF/ANSI 58 covers point-of-use reverse osmosis drinking-water treatment systems, including TDS-reduction performance. | Confirm the exact system model and configuration are certified to NSF/ANSI 58; certification of a component alone does not establish certification of the complete system. | A current certification-directory listing or certificate naming the complete system model and standard. |
| TDS reduction claim | Compare feed-water TDS with treated-water TDS using measurements taken under the applicable test protocol. | NSF/ANSI 58 includes a minimum 75% TDS-reduction requirement for systems evaluated for this performance claim. Verify certification and the claim for the specific model. | Test report or certification documentation stating the TDS-reduction result and test conditions. |
| Calculation | TDS reduction (%) = [(feed-water TDS − treated-water TDS) ÷ feed-water TDS] × 100. | Example arithmetic only: 500 mg/L feed and 125 mg/L treated water gives 75% reduction. This is not a measured result or a product certification. | The original paired readings, units, sampling points, and calculation—not just a percentage in advertising. |
| Test conditions | TDS readings can vary with feed-water composition, pressure, temperature, membrane condition, and system operation. | Compare results only when the sampling and operating conditions are documented and appropriate to the applicable standard or stated test method. | Test method, feed-water details, operating pressure and temperature, stabilization procedure, and sampling locations. |
| Measurement quality | Use a suitable, maintained TDS/conductivity meter and take representative feed and treated-water samples. | A handheld meter reading is useful for operational checks but does not, by itself, prove NSF/ANSI 58 certification or laboratory-tested performance. | Meter calibration or quality-control records, repeat readings, and a dated sampling log. |
| Other contaminant claims | TDS is a broad measure of dissolved substances; it does not identify which substances are present or establish their health risk. | Do not infer reduction of a specific contaminant from a TDS result. Check each contaminant claim and its test or certification evidence separately. | Claim-specific performance data and certification scope for each named contaminant. |
| Home and business fit | Compare rated daily production, storage capacity, recovery/wastewater information, maintenance needs, and expected demand. | Select capacity for the site’s peak demand and source-water conditions. A certification or TDS result alone does not establish suitability for a particular business. | Published capacity and operating limits, installation requirements, replacement schedule, and service plan. |