wvmarle:
20% leakage only? Not too bad. It being low pressure of course helps to lessen leaks.I'm really at a loss on how to detect leaks using moisture sensors. Maybe some form of conductivity sensors, but soil will never dry out unless you're in the desert.
If placed under the pipe (where the leaking water goes) you may even make use of the rain: leaks are where the readings don't change (as it's saturated already).
If most of the leaks are at the joints (i.e. every 12 meters) you'd need a device there, not in between. To collect the data, you could send a probe down the pipe on a weekly basis or so, when in range of a monitoring station it wirelessly takes the reading (you should be able to make it work through a concrete pipe), then at the end of the pipe recover it and read out the data.
Then you have the problem of power supply: batteries run out, and you'll want to have it work "forever" I suppose. That would probably mean installing power cables. If so, your communication problems are also solved: just add another few wires, and talk to your stations over RS485 or so.
You'll also want to make it all really really robust as replacing a failing unit is so expensive!
Yep, 20% that's what i found (At least in Spain). It's not that bad if you're talking about fresh water but it's an environmental problem when talking about wastewater 
The sensor i use is this one: I2C Soil moisture sensor from Catnip electronics on Tindie
It's covered by heatshrink and i coated it with epoxy.
With this sensor I can distinguish a leak even though the soil is not completely dry. More moisture gives me higher reading.
Thanks for sharing your thoughts! I'm gonna google RS485 and try to learn as much as I can about it 