Future water supplies lie in demand management

By: Jeremy Westgarth-Taylor (Founder of Water Rhapsody Conservation Systems and winner of a WWF Green Trust Award)

Water is in the news again, but never has the situation been as dire as today.  Quite simply – Cape Town is out of water. Any new augmentation schemes are not sustainable.

The following are proposed non-sustainable schemes:

  • Damming the Lourens River at Somerset West:  This will add less than one percent capacity to our beleaguered situation.  There are no more rivers that can possibly be dammed to provide any more water for Cape Town.
  • Extracting water from the berg by pumping to the Voëlvlei Dam:  The well-respected head of the Freshwater Research Unit at UCT, Prof Jenny Day, commented that this was a “no-no”.  Already the salinity of the Lower Berg River is rising to unacceptable standards, and any further extraction will make this worse.  The situation of the Lower Breede River is equally parlous.
  • Desalination of sea water:  this is not sustainable as it is too costly on any scale let alone on a large scale.  Costly because each kilolitre of water desalinated from sea water will cost more energy than we have got or we likely will get. Desalination costs eight kilowatt hours per kilolitre of desalinated water.  Further problems of desalination are that a super saline concentrate is returned back to sea, which turns valleys in the sea into a place where neither plants nor animals can survive.
  • Pumping from the TMG (Table Mountain Aquifer):  Already we have seen deep boreholes dry up and collapse in this aquifer and any extraction from this aquifer will have a negative impact on the river systems as this is most likely where the recharge of the aquifer will come from.  These are the same rivers that are now dammed to extinction throughout the Western Cape.
  • Recycling of sewerage effluent:  while this is to be supported, it must be understood that this will not be acceptable to some of our religious groups.  It should also be noted that our sewerage systems are in an unsafe condition, and we need some 6.6 billion Rand to upgrade and build new sewerage treatment works.  Here too energy plays a huge role, as 90% of the running cost of our sewerage treatment works is the energy cost of pumping water around the various treatment sewerage works.  At last check there was only 300 million on any long term budget for upgrading sewerage works.

Grey Water

Garden Rhapsody. A grey water solution by Water Rhapsody.

Director of DWA (Department of Water Affairs) Rashid Khan stresses the use of demand management as the way forward to use less water He also talks of the re-use of on site water but fails to mention “grey water” as a specific.

Grey water [water from baths, basins, shower and laundry] unnecessarily goes in the same pipeline as black water to be treated at sewerage treatment works. All grey water diverted from the sewer system and used for irrigation purposes means far less effluent to be treated.

All of our present problems of water supply would simply go away if everyone could simply use less water.  Halving one’s water demand is easily achievable by: (a) re-using grey water; either for irrigation purposes or toilet flushing; (b) minimizing toilet flushing with a device where the user takes control of the volume of flush and; (c) re-cycling swimming pool backwash water to the pool.

Furthermore there are now huge benefits of rainwater harvesting to supply whole households with rainwater for normal use i.e. for bath, shower, hand basins, laundry, toilet flushing etc.  This makes perfect sense if one considers that – of the water from dams that can be accounted for, 60% of water delivered to the Greater Cape Town area, is used in the home.

If grey water were to be re-used on a large scale we would see a reduction of up to 90% of effluent reaching our sewerage treatment works, saving huge sums of money and giving our sewerage treatment works spare capacity which they don’t have at the moment.

Water Tariffs

Water Tariffs are also set to rise dramatically as a tool to get water consumers to use less water.  The City of Cape Town has a monopoly on both the supply of water as well as the tariffs, except that one may now supply one’s own water by delivering rainwater harvested from roofs to one’s whole household during our winter rainy season.

On top of tariff hikes, water restrictions, etc. any further action by Cape Town, should we run out of water, would be to have water outages as a means to stem demand.   This was used recently in Beaufort West where they got outages for 36 hours at a time.  Making use of rainwater harvesting to supply one’s home would exempt the user from outages, as rainwater tanks double as an emergency feed of municipal water as well.

If there is any further proof that demand management could fix the water supply problems that are upon us, a Water Engineer of Cape Town – Dave Ramsay – stated about ten years ago, that when water restrictions are imposed, consumption comes down.  This should be enough to convince suppliers and users of water alike of the benefits of demand management.

However, he went on to say that once the water restrictions were lifted, demand rises again, but never to the level prior to the implementation of water restrictions.  This is perhaps because to stem demand, the City has historically restricted irrigation with municipal water, so to keep their gardens alive homeowners installed water saving devices, including devices to re-use grey water for irrigation purposes.

Edited by Saving Water

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