you could take the German town Freiburg as an inspiration. They had small canals on the sides of the streets in which they poured the grey water. they also used the water in them to stack fires. --- **Sources**: - [Archäologische Beobachtungen zu den Freiburger Altstadt-Straßen und zur Entstehung der „Bächle"](http://archiv.ub.uni-heidelberg.de/propylaeumdok/43/1/Untermann_Freiburger_Altstadt_1995.pdf) (PDF, in German) > 