Here we argue that decentralised and point of use water infrastructure and technologies are fundamental in delivering health and economic sustainability in rapidly growing cities of the Global South. Further we advocate that research on decentralisation with developing world partners has the potential to catalyse radical change in unsustainable centralised western practices and thus will be mutually beneficial. There has been significant investment by charities and government agencies in developing novel wastewater treatment technologies and many are now close to market readiness. The Asian Institute of Technology in Thailand are piloting a suite of novel market-driven decentralised biological wastewater treatment technologies that were developed with Bill & Melinda Gates Foundation funding. The technologies work but their performance is variable. There is evidence that this is caused by variability in the microbial populations at the heart of the technologies, which are poorly understood. We will work with AIT to characterise and optimise the structure and function of the microbial treatment communities. The aim will be to mitigate the risk of failure by refining the AIT designs and offering rapid low-tech remediation strategies that can be deployed by customers should failures occur.