Cape Town’s Aquifers

Cape Town’s Aquifers

We have three substantial aquifers.  These are the aquifer under Table Mountain, the Cape Flats and what is known as the TMG (Table Mountain Group) Aquifer, which is not the same as the first.  We know that the Cape Flats Aquifer gets recharge every year, but as for the other two, very little is known.

The late Bryan Davies who was one of the beautiful people who were instrumental in the tart up of the FWRU (Fresh Water Research Unit) at UCT and who was highly vocal about his objections to any abstraction from the TMG Aquifer.  His logic was simple:  we do not know when or how long the recharge of the aquifer will be, and where if any recharge is to come from.  If this is to come from rivers, this will then deplete the rivers and any abstraction from our dams for use in the city and farming will be reduced.  Take that!  He believed that the source of the fossil water in the aquifer came from the last ice age.

The quality problems relating to the extracted water from the TMG aquifer are mostly some iron and manganese which both of which leave a bitter metallic taste to the water.  This may easily be removed by oxidising by aerating the water which will most likely happen anyhow as the water may be allowed to flow over some rocky or sandy areas before arriving in a river which leads to a dam, and then water from the dam is chlorinated and flocculated and sent into the pipelines for use in the City of Cape Town.

Cape Flats Aquifer:

 

 

 

 

 

Contractors drilling for water in the Cape Flats

E-Coli: The Cape Flats aquifer has many and different problems.  Many of the older previously outlying areas from the city centre (now sprawling suburbs) had sceptic tanks which allowed the digested human faecal matter to run into soak away trenches otherwise known as “French Drains” for decades.  This provided a natural feed of recharge for the aquifer but with very poor quality water naturally loaded with E-Coli.  Those coliforms are still there, and are waiting for new hosts.  Drink this raw water and expect tummy problems of a very serious nature.  This water may very well kill one especially a baby.

Cape Town sewers are thousands of kilometres underground through the Cape Flats.  No wonder then that there have been regular spills of the raw stuff into the aquifer.  The water in the aquifer moves around one meter per day so in a matter of a few years has moved several kilometres carrying its contaminated company.

Add to all of this old pit latrines, and it would be fair to say that the Cape Flats Aquifer is polluted!

Salinity:  one must never forget that the sea once covered the Cape Flats area.  Parts of the Cape Flats are super high in salty water and the deeper one drills for water in this aquifer the worse is the salinity.

Iron: it is quite astounding how the quality of groundwater differs from place to place and water in a well point or borehole only a few metres apart may have such differing iron content in the water.  Iron rich water may be crystal clear when extracted but allowed to oxidise the iron turns brown and stains everything.

Clay:  some boreholes extract water loaded with fine clay.  The clay forms a colloid and does not easily settle.  Used for irrigation the cleaves of plants get covered with a creamy coloured liquid and dries to a powder when dry.  This water is useless to anyone who has this quality water.

All mixed together:  High salinity often goes hand in hand with iron. This mix is toxic to plants and will kill them.  Any thought of using any of the water with a combination of problems in homes will find the mix very difficult to overcome.

Despite these problems, Cape Town City are drilling boreholes all over the Cape Flats with the intention of using this water and blending it into the water supply of Cape Town.

Lastly the quality of ground water not only differs from place to place, but also remarkably from one season to the next.  The quality is typically worst just before the winter rains when the water table is lowest.

Table Mountain:

The biggest problem of the Aquifer under Table Mountain is the low pH of the water.  This acid water dissolves copper pipes and extended use these start bursting.  The water is difficult to balance and indeed resists balancing with normal practise, and most often needs dosing with strong caustic before the pH can reach acceptable and safe standards.  It must be borne in mind that that copper is a heavy metal and if water with a low pH is used, the copper dissolved in the water may reach toxic levels causing copper poisoning.

Falling Water Tables:

The aquifer at Table Mountain as now porous.  There are now thousands of people extracting water from this mountain the water table is in serious trouble all over the place.  Sea Point:  sea ingress.  Southern Suburbs:  table falling to levels where places no longer get any water at all.  Hout Bay:  water quality shows serious stress.  Constantia:  pH levels are falling needing constant upgrades to methods of balancing the pH.

Does it then make any sense to drill for water and extract this falling resource and ignore and yet throw away the rainwater that falls on one’s roof?  Rainwater is far safer easier and cheaper to harvest that ground water.  The only problem it falls when one thinks one cannot use the wonderful stuff that falls from the sky.  This should not be seen as a problem as rainwater may be used as a supply to the whole household and thus for at least half of the year.  If the Cape Town City Council would only come to the aid of users of winter rainfall for household use,  to get some consideration for their rates for summer / dry season.  The city should in fact look at the entire years supply and divide the years supply into 12 months to get an average use and charge for water at that rate even if this is a slightly higher rate than on the normal monthly basis.  This of course will never happen because the city makes pots of money from the cash cow called water supply. The more water sold the better until we should run out of water which could well happen, and this time – really run out.

The City needs to be very cautious drilling and extracting water from our aquifers.  Constant monitoring the tables and the quality of the water will keep those in charge of this on their feet.

Jeremy Westgarth-Taylor