City of Cape Town’s Reasons for Lowering Pressure to Reduce Usage
The City of Cape Town used to supply what in Europe was considered an extremely high pressure in its mains network to its consumers. It was not unheard of for pressure to spike above 11/12 bar during periods of low demand, such as the early morning. The high pressure was enjoyed by all (bar the municipality) for the power showers, the long reach of the garden hosepipe, and the ability to operate numerous draw-off points simultaneously. However, over the last 20 years the City of Cape Town – due to various prolonged drought cycles, aging infrastructure and a massive increase in demand, to name just a few – has had to reassess its structures.
After organising resources from both the private and public sectors, the City is formulating a water resilience strategy projected to last up to 2035. Learning from previous experiences, they have chosen to institute changes in weighted stages so that any negative results can be addressed and resolved prior to the next phase being implemented. One of the first actions instituted by the City of Cape Town was to lower the pressure of the water flow it supplies to its consumers. Their thinking was simple.
Pressure Management
Municipality decreases the mains pressure it provides its customers → Less flow volume of water released per second when you open your taps → Less water wastage
Although this seems very logical, it has not come without bringing certain new problems to the fore.
The first is the comfort of its consumers. Those used to the older pressure levels had grown accustomed to the comfort of an abundant shower and the ability to utilise various water-using machinery (dishwasher, washing machine, etc.), and now actually have to plan their water usage regime (such as people not showering at the same time, or when garden sprinklers are programmed to operate).
Also, as South Africa had always historically had high-pressure supplies (in relation to continental Europe), South African companies manufacturing for the South African market tended to design products which required higher pressures to operate optimally.
Ceramic Disc Mixers and the Low-Pressure Problem
As we all acknowledge today (except for a small exclusive Victorian market and the RDP sector), most water faucets have now turned to Ceramic Disc Mixer units. These units require a balanced hot and cold water supply into the unit (i.e. x bar hot supply to x bar cold supply); if one supply is greater than the other, it can push the other’s waterflow back and cause cross contamination. But of greater concern to the general South African public is that many of the most popular South African brands will not operate to their potential at low pressures. Although Cape Town stated pressure parameters range from 1–9 bar, many of the plumbing merchants’ home brand ranges are not tested to operate at the lower level – neither are such giants as Cobra nor Isca (as per Google search).
The Real Variable: Demand
Looking at projected climatic trends for the next 20 to 30 years, present levels of temperature and precipitation do not seem to be changing course – and in any case these trends are measured in millimetres of precipitation and tenths of a degree Celsius. After all, as at today we are on average only 8°C warmer than the mean temperature during the last Ice Age 20,000 years ago!
We must face that the main variable affecting our planet is demand from us, homo sapiens.
Although we might not like the measures being implemented by the City of Cape Town, I think we must all agree that this restraint and logic is necessary – and necessary now.
By the City Council lowering ambient water pressure in its network – and after all, if it is that much of an inconvenience to the property owner, it is always possible for them to install their own pressure pump for their own property – it also brings about secondary beneficial effects to help us through this hopefully temporary period.
Leak Detection Through Pressure Management
Lowering excessive network pressure will also reduce the likelihood of pipe bursts and hidden leaks:
- By maintaining a lower and more balanced pressure level, less stress is exerted on the walls of the pipe and there is less movement – expansion and contraction – at the joints, etc., lowering the incidence of pipe bursts. This can be viewed as proactive prevention rather than reactive detection.
- By the installation of PRVs – Pressure Reducing Valves – at pumping stations throughout the grid, the City can manage smaller and easier-to-control pressure zones. The pipes will therefore not be exposed to unnecessarily high stress, particularly during night-time or low-demand periods (see above point).
- By increasing the specialist leak detection units, who can – via both visual inspection and manual techniques – proactively cover significant areas, especially in rural and between urban areas. This tactic over the last year has proven its worth, with over half of its 10,000 km piping network inspected and over 900 leaks traced, saving an estimated 4,000,000 litres of processed potable water per day.
- Pressure-measuring apparatus between pumping/booster stations to signal leakages.
- These leak detection units are being modernised with digital monitoring and acoustic, telemetric, real-time apparatus to complement the “feet on the ground” visually looking for evidence of leaks.
- A highly detailed reporting database of prioritised areas, based on the age of the laid piping, infrastructure, historical burst rates and unusual pressure hot spots.
- The City has also indicated that the Leak Detection Division isn’t a one-off until the end of the present planned Water Strategy — they will absorb it as a continuous programme and interweave proactive scheduled pipe replacement and valve maintenance, as well as constantly adopting feasible and measurable future anti-leakage technology, especially in the more rural areas.
Bottom Line
Cape Town has seen the looming phantom of “Day Zero” and is working proactively to minimise “non-revenue water loss” (water lost through leaks) and to protect our precious water resources in our water-scarce environment by introducing a multi-faceted plan of action.
We welcome you to our website www.amanzirms.co.za/blog/ or www.amanzirms.co.za/technical-insights/ for more informational articles.
