I use tap water that is safe to drink, do I have to treat the water ?
1) Water that is safe for an adult human to drink can kill thousands of species including fish.
2) Treating the water is not a yes/no question. It's more like a "under what conditions can I get away with doing or not doing something" question.
Water that is safe to drink (for humans) contains chlorine or chloramine in an amount that falls within a certain range. That range can be---but isn't always---lethal to fish. It depends on the fish, how much of that water is in the total water supply, and other factors (like the fish's health, the water oxygen level, etc.) Even if the water isn't immediately lethal, it can harm the fish on a long term basis and cause an earlier death. People who live far from the water supplier get a lower dosage of chlorine than people nearby.
So using other aquariums as a guide is fraught with danger and perhaps not meeting the criterion you have for raising and caring for your fish.
If I had expensive, emotionally important wet pets, I'd spend extra effort to make sure the water was not potentially poisonous. OTOH, if I had many tanks and far too many guppies, I might not even care. Most people sit somewhere in between those obvious extremes. So it's your call. A slow drip with a lot of agitation or spray with well oxygenated water and very hearty fish might not need a treatment for chlorine. But it's still really, really cheap to eliminate the issue altogether, so for me, I'd treat the water. But, I'm very conservative, borderline OCD. For others, who have years of experience with a stable system, they know that as long as things don't change, it's not needed and they have safety procedures in place that might mitigate that risk if things do change.
You have to look at your conditions and fish and judge how risky you care to be. Research your fish, your water supplier and examine your priorities.