OK, now can you compare the tap water results with the water data from the municipal water authority? They may have a website, and if so, water data is usually posted somewhere. This is worth doing because it will confirm (or refute) your test strip results for the tap water.
The results from the tap confirm the water authority. However, after leaving the strip out for a while, the pH faded towards 7.8. Should I trust this value or the value that I got initially from the tank?