As you know, there are people who decry conventional sewerage, saying it’s simply not sustainable. Of course, we know that it’s too expensive in low-income areas in developing country towns and cities − but is it sustainable in low-income urban areas of the industrialized world? Well, here in England we’ve sustained conventional sewerage for around 150 years − which tells us that it’s been sustainable for this period (well, perhaps not all this period as it's only fairly recently that we've prevented adverse effects on the receiving waters through good wastewater treatment). And it’s affordable: the average annual sewerage charge in 2007/08 was GBP 162, or GBP 3.12 per week (details here) which is only 0.7% of the 2007 median male income of GBP 457 per week, and only 1.3% of the median income of the ‘bottom 10%’ of GBP 252 per week (details here). For the vulnerable group of single pensioners the sewerage charge is 3.7% of their basic state pension of GBP 83.30 per week (details here).
Of course, the fact that conventional sewerage has been sustained for the past 150 years or so doesn’t necessarily mean that it’ll be sustainable in our climate-changing future in which water will become much scarcer. However, we can easily reduce our in-house water consumption without fear of the reduced wastewater flow causing blockages in the receiving sewer − here’s what the Environment Agency (the environmental regulator for England & Wales) says in chapter 1 of its 2007 publication Conserving Water in Buildings:
As the amount of water we use has increased considerably since most of the UK’s sewers were built, sewers are no more likely to become blocked due to less water being used to flush the toilet or indeed due to any other water efficiency measures.
So we’ll be sustaining conventional sewerage for years to come!