How did ancient aqueduct engineers get around the problems of leaks and evaporation or even absorption by the stone? It would seem that after travelling a long distance, there wouldn’t be much water left at its destination. And what kinds of levels did they use, to maintain a proper gradient?

Most aqueducts were lined with clay, so they didn’t leak much. They also weren’t above-ground channels. Of the entire system of aqueducts servicing Rome, for example, only a few miles were above ground at all, and those were sealed channels atop archways.

Sure they lost water. As long as they managed to get enough water it was acceptable loss.

We still have the same problems today with municipal systems in the US for every 5 gallons of potable water delivered we lose 1 gallon to leakage. Most of that is underground leaks that are rarely discovered. It’s enormously expensive to operate our water supply with that kind of inefficiency but it’s deemed acceptable because that’s the way its been done for decades.

The Romans were very good engineers, getting the grade right was no real challenge for surveyors of the time. Water makes a pretty good level.

Yes, most acqueducts were build underground.
By the way, Romans weren’t the only acquedut builders. Most peoples in Eurasia had some form of Aqueducts, Greeks, Chinese, Persians, and even since the time of Solomon there were these kind of civil works! The Roman improvement was the arch applied to acqueducts. In the Americas, Nazcas and Incas build some impresive underground acqueducts as well. And Spaniards build a few acqueducts in Roman style in Mexico.

Romans weren’t that concerned with conserving water.

Remember that many Roman fixtures (and aqueducts themselves) had no shutoff control. Those Roman fountains ran continuously (no recirculating pump), so water was constantly running down the drain.

To reiterate the point, getting aqueducts level is pretty easy: For the rough leveling, basic surveying with a hanging weight (plumb) level and your eyes is good enough (‘plumb’ being Latin for lead, which is what the hanging weight was made of).

For the fine leveling, just let some water run in the top, and see where it goes. If it pools somewhere, that’s a low spot and you need to raise it (or lower the bit just beyond it). There are probably some interesting tricks they used, but that’s the basic idea.

You just start the water from a point higher than your destination, and it’s all downhill from there.

Gradient was important: Too fast/slow, and their was clogging, silt build up and some blowouts if you had to go down/up valleys with the wrong slope.

The techniques were known/reliable, but the gist of the engineering wasn’t just to create “a” grade, the gist of the engineering was to create* “the”* grade.

They also had waterproof concrete (made by adding pozzolana ash), and also concrete that actually set underwater (used mainly for making port and dock facilities). They may have lined the aqueducts with clay too, but I would have thought that having concrete would be the more important factor.

From the start to the final destination, this is true, but the Roman aqueducts did have someuphill sections along the way.