In my modeling scenario, wastewater is routed to and directly reused by two demand sites (using green transmission links), and the (remaining) wastewater is routed to a wastewater treatment plant (using red return flow links). How can I specify the value or fraction of each wastewater flow?

In my model, I fixed the maximum flow volume and maximum flow percent of demand for transmission lines connected to the two demand sites. However,
not enough wastewater was supplied to the demand sites, and some portion of the wastewater went to the return flow. This causes unmet demand condition. I would like to decrease the return flow rate such that the water demand of the demand sites are met.

How can I solve this problem?

WEAP will automatically try to route enough wastewater from the first demand site to fully satisfy the demand at the other two demand sites. You do not need to fix the maximum flow volume or percent of demand in the transmission links.

Jack