Treated tap water is generally no problem unless there are extreme conditions. But if you are not assured, there are several water quality parameters you can try to test.
Residual chlorine: Water plants use chlorine to disinfect and kill bacteria and viruses. After passing through the water supply pipe, there is generally no more than 0.5 mg/L of residual chlorine to ensure that the water in the pipe will not be contaminated by bacteria. If the residual chlorine is too high, there will be a pungent smell of disinfectant water, if it is too low, the water supply pipe may still be contaminated by bacteria. You can buy residual chlorine detection reagents for your own testing.
TDS: Total dissolved solids. Taobao has many TDS detectors. Generally speaking, tap water readings in the hundreds of mg/L are normal. But TDS is only an indicator of the total amount of ions in the water. These ions may be heavy metals or beneficial minerals. So it can only be used as a reference. When the reading is too high, you can suspect that the water quality has suddenly changed.
Hardness: calcium ion and magnesium ion. Low hardness will not have too much scale.