We usually do as you've said a backpack with water and a collapsible bowl, however there are usually plenty of places to get water for nothing.
We take our guy on 30-60 minute walks on occasion as he's still young and he is a long haired breed, however if we know our route will take us to rivers, lakes, streams etc, we won't always take water, but allow him plenty of time to stop and drink by the water. A bonus is many shops and pubs around us have dog water bowls outside, and one lovely house has one as well for passing walkers to allow their dog to drink!
I suppose it depends on how much you want to carry, but if you can't guarantee a source on route a bottle would be necessary, as a hiker I don't notice the extra weight much. You could invest in a bottle with the bowl attached that hook via a carabiner, but these are prone to leaking.
Another point to make is if you can't keep your hand on the floor (tarmac, sand, bare earth) for a good few seconds in hot weather, don't force your dog to walk on it.
I believe it better to take it and not need it, than leave it behind and find yourself wanting.