Most people assume the water arriving at their tap is a constant. It is not, and the variation is larger than you would guess.
What moves, and when
- Monsoon dilutes groundwater. TDS and hardness fall, but surface runoff can raise turbidity and microbial load.
- Summer concentrates it. Water tables drop, dissolved solids rise, borewells pull from deeper and harder strata.
- Municipal switching matters most. Many Indian cities blend sources seasonally, so your supply can change origin entirely without notice.
- Tanker top-ups during shortages arrive from wherever the tanker filled up.
A purifier tuned to one profile will behave differently on another. This is why a unit that impressed on installation can quietly disappoint six months later.
Why consistency is the honest metric
This is why the IAPMO series varied the feed deliberately rather than testing one convenient sample — six-fold on dissolved solids, four-fold on hardness.
Output stayed between 63 and 192 mg/L TDS, hardness between 12 and 29, and pH between 6.75 and 7.21 throughout. Rejection rose as the feed got worse: 53% at 250 mg/L, 93% at 1,500.
Ask for performance across a range of feed water, not a single figure. A number quoted without the input it was measured from tells you very little.
What to do about it
Watch your TDS reading over time rather than at one moment. A sudden move usually means the source changed — useful to know, and the reason a live display is worth more than a one-off showroom demonstration.
