Campus Study of the Impact of Ultra-Low Flush Toilets on Sewerage Networks and Water Usage

Water demand management often focuses on quantifying the benefits of water efficiency rather than the potential impact of reduced flows on the sewer network. This study assessed the impact of a high-density deployment of ultra-low flush toilets (ULFT). A pre-installation washroom survey was carried out in July 2018. Water demand and sewer network condition were assessed ahead of the installation of 119 ULFTs and a real-time monitoring system across seven buildings on the University of Exeter campus. ULFTs were flushed 257,925 times in 177 days saving an estimated 2287 m(3) per annum (compared to traditional 6 litre WCs). The annual cost saving of this reduction is approximately 12,580 pound/annum, assuming a volumetric cost of 5.50 pound/m(3) of water. Mean discharge to the sewer network reduced by 6 m(3)/day. In the six-month period, 95 maintenance issues were reported, equating to 1 in 2700 flushes (0.037%). However, the frequency of incidents decreased after an initial commissioning period. There is no evidence, from blockage reports or photographs of manhole flow conditions, that the risk of blockage in the sewer network increased as a result of the ULFT installation programme.

Automated summary

This study assessed the impact of high-density deployment of ultra-low flush toilets (ULFT) on water efficiency and sewer network condition, finding that ULFT installation can save water resources and reduce the burden on sewer networks. Despite 95 maintenance issues reported post-installation, the overall frequency of incidents decreased over time.