related- was there any policing of the aqueduct, considering how important it was? I mean, stopping people from dumping random things into it, pooping in it, etc.

I might be misinterpreting your question, but it sounds like you are asking if people used boats or swam in the aqueducts. Is this correct?

The trouble is that an 'aqueduct' is not simply a viaduct that water travels through. Indeed, you generally wanted, for security and maintenance purposes, as little to be built on arches as possible. Rather, aqueducts were long-distance pipes, moving water using gravity by way of an almost minuscule gradient, and designed to be fully enclosed. And the safest, lowest-maintenance place to lay a pipe? Underground.

A look at this map of the section of the Nîmes aqueduct near the famous Pont Du Gard of Provence illustrates my point exactly – the channel cuts through a large hill, zigzagging as it goes. The situation with the Roman supply was similar. The oldest aqueduct, the Appia, roughly 16.5km long, ran on arches for only 90m before reaching the city walls. The least underground aqueduct, the Aqua Julia, ran above-ground for all but 3 of its 23-kilometre length, but was anomalous in this regard.

So we've established that aqueducts were largely underground and thus a pretty horrible way to travel. But have we even established it was possible to travel through them? Well, I have actually been inside the Pont du Gard, and this is roughly what I saw (not my picture but it illustrates my point exactly). See how the sides 'pinch' inwards at the bottom? That's not actually original material – it's mineral deposits left behind after centuries of use, and you can tell where the water level generally was by the height of these deposits – and it's quite obvious that the space between the top of the water and the ceiling was maybe about a foot. It would be pretty hard to swim down that, let alone boat up it.