After the Persian-Avar siege of 626, no mentions of repairs are made until Constantine V (766).

Crow et al. 2008 argues that these years were not completely dry. If the Valens and Hadrian Waterways were two separate systems, it is more plausible that only the long distance (Valens line) suffered the most from the damage inflicted by the siege of 636. The Hadrian line with sources from the Belgrade Forests and Cebeciköy continued to function.

During this period of reduced supply, the source of the water transported by the Valens aqueduct bridge may have changed too. Even though the link between the two channels from the Valens aqueduct bridge and the water sources are not exactly clear, Crow proposes a theory that it must have carried water from Thrace (Vize?). After 626, this source fell out of use, and the Valens aqueduct bridge may have carried a reduced supply consisting of water from Halkalı instead.