Thailand’s flood crisis in 2011 brought damage to many areas in Thailand. Especially in Bangkok, the water could not drain into the Gulf of Thailand at that time. This paper aims to apply two algorithms, consisting of the generic augmenting path algorithm and the labelling algorithm, in order to determine the maximum flow of water from the north of Bangkok to the Gulf of Thailand. The flow of water in Bangkok is represented by network flow. Rivers and canals are represented by nodes and arcs. Labelling and the generic augmenting path algorithms were used to find the water route from a source to a sink and maximum water flow respectively. The results showed that the maximum flow in Bangkok was 228,960,000 cubic meters per day.