Abstract: Water that meets standards when it leaves the plant does not mean the water at your tap is the same. After passing through tanks, reservoirs and old pipes, endpoint water may change. Using a multi-parameter test pen at your own tap, and comparing across different times, different floors and different residential compounds, is the most direct approach.
Keywords: how to test secondary water supply quality, water quality testing in old residential areas, is tank water clean, what to do when tap water turns yellow, endpoint water testing
One-sentence answer: What you drink is the "endpoint water" at the tap, not the water leaving the plant. If you want to know whether there is a problem with the secondary water supply, test at your own tap, focusing on turbidity and organic matter. The Water Detective 9 parameter version automatically saves the time and location after testing, and can also compare with nearby residential compounds on the water quality map.
Why endpoint water changes
Many high-rise buildings and old residential areas use secondary water supply: tap water first enters the residential compound's tank or reservoir, then is pumped upstairs. If the tank is not cleaned in time, sediment accumulates; old pipes may rust; and if water sits in the tank for a long time, residual chlorine also decreases. Even within the same city, or even different buildings in the same residential compound, water quality can differ.
The most worthwhile situations to compare
| Comparison | How to test | Main things to look at |
|---|---|---|
| First glass in the morning vs after running the water | Draw the first glass in the morning, then run the water for 1-2 minutes and draw another glass | Turbidity, UV254 |
| Before a water outage vs after supply resumes | Measure first thing after water supply is restored | Turbidity |
| Before vs. after tank cleaning | Measure once before and once after each property cleaning | Turbidity, COD, TOC |
| Rainy season vs. dry season | Measure at a fixed time each week and save the records | All 9 items |
| Your own home vs. relatives' and friends' homes, other communities | Use the same pen to measure, or check the water quality map | Overall score |
What to do if an anomaly is found
- Let the water run for a few minutes before measuring to rule out the effect of water standing in the pipes.
- Retest over several consecutive days to see whether it is an occasional occurrence or consistently high.
- Take a screenshot of the history in the mini program and report it to the property management or water supply department, requesting that the water tank be cleaned or a water sample be submitted for testing.
- You can install a pre-filter or water purifier at home, then use the pen to compare the filtration effect (see section 4).
Frequently Asked Questions
Q: Why is tap water yellow and smelling of rust? A common cause is rust in old iron pipes, or sediment in the pipes being stirred up after a water outage; turbidity usually rises noticeably. First run the water, then test again to see whether it returns to normal.
Q: What is the water quality map? The test results of Water Detective users are aggregated by location on the water quality map in the mini program, so you can compare water quality in your own area with that in other regions.