The advice was well given (thanks Chesherca
), and should be considered by most of us. It depends where you live obviously, as the source water may or may not be affected by various things. And water can change seasonally.
Here in Vancouver our water comes from three huge lake reservoirs up in the Coast Mountains. When it rains very heavy as it does in the Spring and Autumn particularly, we can see more sediment in the water. This in itself is not harmful. But in some areas of the continent, the water authority might have different sources and switch from one to another at such times, and parameters can change accordingly. Or various substances might be added at such times to deal with issues.
Another possible issue can be increased treatment for bacteria. Additional chlorine, adding chloramine, etc., is sometimes used sporadically. Always using a good water conditioner protects against this, as published notices may not been seen in time.
Unless you have a track record over many years to go by, one shouldn't assume the water coming out of the tap will always be the same.