Wireless Sensor Networks (WSNs) are energy constrained. Every operation, particularly the use of radio, reduces the energy reserves of nodes. The aim of this work is to improve the useful network lifetime of a WSN, which we define as being from the time when the network is activated to the time at which it is no longer able to carry out its assigned task. Routing protocols try to preserve lifetime by being energy-aware or load-balancing. However, these approaches tend to behave non- cooperative across multiple sources. We present a heuristic known as node reliance, which indicates the degree to which nodes are relied upon in routing messages from sources to sinks. We hypothesise that by using this heuristic and avoiding nodes of high reliance, the useful network lifetime of the network can be extended.