My question is more related to when did the Roman aqueducts transitioned from being a revolutionary infrastructure tool, to being left idle and eventually becoming ruins? Did people of later civilizations, in the Dark Ages, Medieval ages and Renaissance have any idea what the roman aqueducts were, or did they just assume the aqueducts were just some other ruin of the long gone Roman Empire?
A lot of Roman aqueducts were used for a long time, well after the fall of the Roman Empire, even though the amount of water they supplied often decreased due to low maintenance. Basically you could say that there were always people who knew what the Aqueducts were made for, the knowledge was never really lost.