Read this very illuminating paper: Securing 2020 vision for 2030: climate change and ensuring resilience in water and sanitation services, by Guy Howard, Katrina Charles, Kathy Pond, Anca Brookshaw, Rifat Hossain and Jamie Bartram, which has been published in the Journal of Water and Climate Change [2010: 1 (1), 2−16]. Here’s the Abstract:
Drinking-water supply and sanitation services are essential for human health, but their technologies and management systems are potentially vulnerable to climate change. An assessment was made of the resilience of water supply and sanitation systems against forecast climate changes by 2020 and 2030. The results showed very few technologies are resilient to climate change and the sustainability of the current progress towards the Millennium Development Goals (MDGs) may be significantly undermined. Management approaches are more important than technology in building resilience for water supply, but the reverse is true for sanitation [emphasis added]. Whilst climate change represents a significant threat to sustainable drinking-water and sanitation services, through no-regrets actions and using opportunities to increase service quality, climate change may be a driver for improvements that have been insufficiently delivered to date.
This is what the authors say about unconventional sewerage:
Unconventional sewerage (including ‘condominial’ [i.e., simplified] and small bore [i.e., settled] sewerage) is more resilient that conventional sewerage. Small-bore and condominial sewers use less water than conventional sewerage and as a consequence they are less vulnerable to decreasing water availability. Modified sewers will still be at risk from damage from floods and other extreme events.
Unfortunately no mention of low-cost combined sewerage – which we might expect to become more widely used as the incidence of flooding increases.