The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia

Abstract

The similarities in climate and geology offer water resource managers in Cape Town and Perth an opportunity to learn from each other’s experiences. While Cape Town relies mostly on surface water for supply, Perth uses 50% groundwater for its domestic and industrial use. It is proposed that certain aspects of Perth’s water supply infrastructure could successfully be transposed for the exploitation of Cape Towns’ groundwater resources. In Perth private boreholes is used to tap a shallow phreatic aquifer for garden irrigation. The Government of Western Australia encourages this practice. Cape Town has an opportunity to use water from the Cape Flats Aquifer in a similar manner. In this paper the use of the Cape Flats Aquifer for private garden irrigation is evaluated. By encouraging private landowners to develop private wells, large savings could be made in the amount of treated bulk water supply required by Cape Town. The Cape Flats Aquifer has the potential to meet a large part of the city’s garden irrigation requirements. Though the impact of pollution on water quality remains uncertain and a concern, the general quality of water in the aquifer is adequate for irrigation requirements. If the use of private garden boreholes is to be successful, education of the public will be vital. It is envisaged that the City of Cape Town and the Department of Water Affairs and Forestry in partnership with private, education and research institutions take the lead in such education and the development of appropriate legislation and guidelines.

Full text

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 331
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth,
Western Australia
I. C. SAAYMAN1 and S. ADAMS2
1Water Programme, CSIR, PO Box 320, Stellenbosch, 7599
2Groundwater Group, Earth Science Department, University of the Western Cape,
Private Bag X17, Bellville, 7535
1 isaayman@csir.co.za
ABSTRACT
The similarities in climate and geology offer water resource managers in Cape Town and Perth an
opportunity to learn from each other’s experiences. While Cape Town relies mostly on surface
water for supply, Perth uses 50 % groundwater for its domestic and industrial use. It is proposed
that certain aspects of Perth’s water supply infrastructure could successfully be transposed for the
exploitation of Cape Towns’ groundwater resources. In Perth private boreholes is used to tap a
shallow phreatic aquifer for garden irrigation. The Government of Western Australia encourages
this practice. Cape Town has an opportunity to use water from the Cape Flats Aquifer in a similar
manner. In this paper the use of the Cape Flats Aquifer for private garden irrigation is evaluated.
By encouraging private landowners to develop private wells, large savings could be made in the
amount of treated bulk water supply required by Cape Town. The Cape Flats Aquifer has the
potential to meet a large part of the city’s garden irrigation requirements. Though the impact of
pollution on water quality remains uncertain and a concern, the general quality of water in the
aquifer is adequate for irrigation requirements. If the use of private garden boreholes is to be
successful, education of the public will be vital. It is envisaged that the City of Cape Town and the
Department of Water Affairs and Forestry in partnership with private, education and research
institutions take the lead in such education and the development of appropriate legislation and
guidelines.
Keywords: Cape Flats Aquifer; garden boreholes; groundwater management
INTRODUCTION
Groundwater has played an important role in the economic and social development of both South
Africa and Australia. The history of water resources development in the two countries has resulted
in disparate emphases on the present day use of groundwater. While water supply in Cape Town
has largely focused on the use of surface water resources, Perth largely uses groundwater for
domestic water supply. As a consequence of its focus on using groundwater, Perth has seen a
proliferation of domestic boreholes used for garden irrigation. This strategy has resulted in savings
in the city’s treated water use. An opportunity exists for Cape Town to implement a similar strategy
as a means of more effective water resources management.
This paper evaluates the feasibility of using privately owned boreholes and wellpoints in the Cape
Town Metropolitan Area for garden irrigation. In most of the suburbs in the City of Cape Town
water applied to household and public gardens, sports fields and recreational areas constitutes a
large part of the city’s annual treated water use. In Perth the use of garden boreholes as an
alternative to potable water for garden irrigation is successful. Cape Town is increasingly being
faced with the water shortages and a rapidly growing population. New and innovative strategies
are thus required to address the city’s water resource challenges. The similarity in climate and
geology that Cape Town shares with Perth offers it a unique learning opportunity. One such lesson

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 332
may be that the use of garden boreholes can be an effective measure in sustainable water
resources management.
Geographical Setting
Cape Town and Perth are located on a similar latitude and share a common climatic regime
(Figure 1). Located at the southern tip of Africa, Cape Town finds itself surrounded by ocean and
prominent mountain ranges. Reaching heights of up to 2000 meters above sea level these
mountains provide a natural barrier to rain bearing frontal systems approaching the African
continent from the south Atlantic. As a result, high rainfall is recorded on Table Mountain and in the
high mountains found to the north and northeast of Cape Town. Values recorded vary between
about 1800 mm/annum on Table Mountain to about 3800 mm/annum in Jonkershoek and near
Franshoek (Le Maitre, pers. comm., 2001, Wicht, et al., 1969).
The topographic low, located between Table Mountain and the Drakenstein and Hottentotsholland
mountains, is known as the Cape Flats. Average rainfall over the area of the Cape Flats is much
less than in the surrounding mountains, and averages about 600 mm per annum, with most rainfall
occurring during winter (see Figure 2). Large parts of the Cape Flats are covered by urban
development. Today most of the city’s population lives within the area of the Cape Flats. Based on
1996 census figures (Statistics South Africa, 1996) the 2001 population of the larger Cape Town
Metropolitan area was estimated at just over 3 million (Dorrington, 2000).
The city of Perth is located on the southwest corner of Australia. With a population of 1.4 million it
is by far the largest urban centre in Western Australia. With a relative abundance of land, most of
the population live in detached houses with large gardens. A Mediterranean climate characterized
by wet winters and dry summers means that most households require garden irrigation for large
parts of the year. The city is located on the highly permeable Swan Coastal Plain, of quaternary
sand and limestone, which is separated from the crystalline rocks of the Darling Range by the
Darling scarp. Average annual rainfall for Perth ranges between 700 and 1300 mm per year (see
Figure 2), while average annual evaporation is about 1800 mm per year (Sililo and Appleyard, in
print).
Perth
Cape
Town
Figure 1: Locations of Cape Town and Perth

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 333
0
20
40
60
80
100
120
140
160
180
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Avg. Precipitation (mm/month)
Cape Town Perth
Figure 2: Average monthly precipitation in Cape Town and Perth. (Source: South African
Weather Service and Australian Bureau of Meteorology)
HYDROGEOLOGY
Cape Town shares with Perth the occurrence of an unconsolidated shallow aquifer beneath the
city. In Cape Town it is known as the Cape Flats aquifer, while in Perth similar deposits are found
within the Swan Coastal Plain. The unconsolidated sediments of the Cape Flats Aquifer were
formed by alluvial and eolian deposition. The average thickness of the Cape Flats Aquifer deposits
is about 30m. The water table is shallow, ranging from a few centimetres below ground surface in
winter months to about 4m in summer. A secondary hard rock aquifer is found below the primary
unconsolidated aquifers consisting of Malmesbury shales and intrusive granites.
Conversely, the Swan Coastal Plain consists of highly permeable sand and sand/limestone dunes
(Appleyard, et al., 1999). These superficial sediments extend to a depth of about 100m with the
average depth being around 50m. This surficial aquifer is underlain by an extensive sedimentary
basin containing aquifer units that to a depth of up to 3000 meters.
CURRENT STATUS OF WATER SUPPLY
Cape Town
Present water resources management in Cape Town has been largely shaped by the abundance
of surface water resources in the form of perennial streams that have their origin in the mountain
ranges. With the establishment of a European settlement at the Cape by Dutch mariners in the
17th century, their choice of settlement was based on the availability of surface water resources.
Most of the water in the Cape Town Metropolitan area is derived from surface water sources.
Some municipal departments and private institutions do use groundwater and reclaimed sewage
water for irrigation. However, the use of reclaimed water is often more costly than groundwater, as
it usually requires treatment to an acceptable quality before use, and require additional
infrastructure (such as separate pipelines and pumping stations).

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 334
Perth
Perth is a growing city that experiences a continued increase in water demand. Presently the city
relies on surface reservoirs and groundwater for domestic supply. Annual domestic consumption is
about 250 million m3. Of this 50 % is derived from groundwater. However, it is estimated that an
additional 184 million m3 is abstracted from 150 000 private boreholes for garden irrigation (Water
and Rivers Commission, pers. comm., 2001, Appleyard, et al., 1999). It is estimated that 1 house
in every 4 has a private borehole that is used for garden irrigation (Appleyard, et al., 1999). Many
of these boreholes were drilled during the water restrictions of the late 1970s, and reflect the value
that is attached to private gardens. Through the use of private boreholes a great weight has been
taken off the scheme supply. In this way the city saves in the amount of treated supply needed,
thus extending the life of water supply schemes.
The use of private boreholes has not been without problem. Of particular concern is the
environmental impact of over-abstraction. One reason for this is that individuals with private
boreholes tend to use more water than those using mains water for gardens. On an average 1000
square meter house block water use for garden irrigation from mains supply ranges between 300-
600 kL/year, compared to about 1000 kl/year average borehole abstraction Water and Rivers
Commission, pers. comm., 2001).
The private boreholes are primarily used for garden irrigation and abstract water mainly from the
shallow unconfined aquifer. The City’s groundwater supply is abstracted from both the unconfined
aquifer and from deeper semi-confined aquifers. The boreholes drilled into the deep semi-confined
aquifers often exceed depths of 800m. The quality of water in both the unconfined and the deeper
aquifers is generally good, with total dissolved solids content below 250 mg/L (Appleyard, et al.,
1999).
Garden boreholes play an important role in the city’s water supply infrastructure. Through the use
of private boreholes the city’s water supply burden is lightened, saving other water resources and
money. Despite the free access that private citizens have to the Perth coastal plain aquifers,
concerns over environmental impacts and a period of exceptionally dry summers has resulted in
Perth water authorities imposing restrictions on water use, irrespective of its source. Such
restrictions include appropriate garden watering times, with a ban on daytime sprinkler use.
GARDEN BOREHOLES AS AN ALTERNATIVE
The experience of Perth in the use of private boreholes for garden irrigation has been a good one.
With so many similarities between Perth and Cape Town it begs the question on whether a similar
initiative in Cape Town would be of benefit to the city.
The use of private boreholes for garden irrigation has in Perth resulted in a reduction in the amount
treated domestic water used. The increased use of private garden boreholes in Cape Town would
similarly result in less treated domestic water being used in garden irrigation. It is estimated that
about 30% of the treated domestic supply to Cape Town water users is applied to garden irrigation
(Parsons, 2000). With annual water consumption of about 300 million m3, the potential water
saving that could be achieve should only groundwater from private wells be applied to gardens
would thus amount to about 90 million m3. The potential monetary saving to the city that this
represents is vast. Such saving result from the smaller amounts of water that will be pumped and
treated, as well as in reducing the need to invest in new bulk water supply schemes.
The fact that Cape Town receives winter rain makes it an ideal candidate for groundwater
abstraction during the dry summer months. This would relieve stress on other water sources during
the dry part of the year. With winter rains the levels in the aquifer should recover, if the aquifer is
not over exploited. By lowering water levels in summer storage in the aquifer is increased, which
reduces the risks of flooding in some of the low-lying parts of Cape Town.

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 335
In encouraging abstraction from the Cape Flats Aquifer concern about the potential of the aquifer
to meet supply will have to be addressed. Parsons (2000) quotes the estimated potential of the
Cape Flats Aquifer at about 53 million m3 per annum. If further studies show this to be correct, then
the Cape Flats Aquifer has the potential to meet a significant portion of the city’s garden irrigation
demand. The sustainable yield of the aquifer could be increased through the artificial recharge of
wastewater. Each year about 190 million m3 is discharged to the city’s rivers. Though yields vary
within the aquifer, even a lower end yield of 2 m3/hour would be sufficient to meet the irrigation
requirements of most private borehole users. This means that most of the city’s suburbs is in a
position to abstract reasonable quantities of water from the Cape Flats Aquifer.
One concern with developing large-scale abstraction is the potential impact it may have on
groundwater dependent ecosystems. Of particular concern is the impact of abstraction on wetlands
that depend on groundwater discharge. A system to address this concern has been developed in
Perth, where similar groundwater dependent wetlands exist. This has been done through the
establishment of groundwater abstraction zones, which are classified in terms of vulnerability and
recharge importance. Within sensitive zones no activities that may degrade the water quality
and/or quantity is allowed. Water managers should also guard against potential degradation of
water quality within the aquifer as a result of seawater intrusion or the induced inflow of poorer
quality water.
Before the widespread use of private garden boreholes is initiated, an evaluation of the quality of
water within the aquifer and its potential health risks will have to be evaluated. Some concern
exists about the degradation of the aquifer by industrial, commercial, informal settlement and
waste disposal activities (Fraser and Weaver, 2000b). It is however accepted the irrigation water
quality requirements are widely satisfied (Fraser and Weaver, 2000a).
WHO SHOULD DRIVE THE CAMPAIGN?
The Department of Water Affairs and Forestry (DWAF), as custodian of the country’s water
resources and the City of Cape Town should promote the efficient use of garden boreholes. An
important aspect in promoting private garden borehole use is public education. It is proposed that a
partnership be formed with the private and public sectors as well as nongovernmental and
education institutions to educate and promote the use of groundwater. Policies should be
developed by the DWAF and the City of Cape Town for the use of garden boreholes that are
aligned to National Water Strategies and Policies. Guidelines should also be developed for the
efficient and responsible usage of garden boreholes.
Any individual who wishes to install a garden borehole should need to apply to the relevant
authority for permission to install a borehole. The applicant should be legally bound to adopt an
approved technical design. The technical specification would specify the depth to which a borehole
may be drilled, the type of material to be used and the pump capacity (in order to control
abstraction) for any particular area. A GIS database needs to be developed to spatially record data
and decisions. The regulatory authority should ideally provide an advisory service, which could aid
in the fostering of a good relationship with the public. After the completion of a borehole the
relevant authority may inspect the completed borehole and approve its use. The data obtained
during the construction of the borehole should then be loaded on the GIS database.
CONSTRUCTION
The installation of garden boreholes is fairly simple in sandy aquifers. Where the water table is
close to the surface and low abstraction rates are required, shallow boreholes can often be
installed using jetting. Jetting is a technique whereby borehole screens are forced into the ground
using pressurized water. Percussion drilling is the favoured technique for drilling in hard rocks. This

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 336
may be necessary in areas where substantial iron concretions, known as ‘Koffieklip’ occur. Slotted
PVC casing is preferred as construction material because of its light weight, low cost and
durability. Depending on the depth to the water table, the borehole may be equipped with a
submersible or surface pump. The structure of a completed borehole is shown in Figure 3.
WATER QUALITY
The quality of the groundwater in the Cape Flats Aquifer is generally fresh due to the high recharge
rates. Water samples taken from the University of the Western Cape borehole site show a fresh
groundwater character in the primary aquifer and a slightly brackish water in the Secondary
Malmesbury aquifer at depth (Table 1).
Table 1 Water quality of the two aquifers tapped by the UWC borehole site and from a general
study.
Parameter Primary Aquifer Secondary Aquifer Gen. Water Quality (Fraser
and Weaver, 2000a)
Na 25.46 217.14 57
Mg 11.68 12.50 11
K 4.62 3.29 1.5
Ca 146.42 22.63 95
Si 0.37 1.09 -
Fe 2.29 0.14 -
Cl 34.50 308.15 99
HCO3 15.80 162.30
NO3-N 0.5 2.4 <0.1
pH 4.9 7.0 7.7
EC (mS/m) 78 128 78
All values in ppm unless otherwise indicated
Surface Seal
(
Cement
)
Gravel Pack
(Optional)
Aquifer
Material
Slotted Casing
(PVC)
Figure 3: Typical constructed borehole in a sandy aquifer.

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 337
The quality of the groundwater is excellent, apart form elevated levels of iron in the primary aquifer.
When used for irrigation the iron may result in staining on walls and pavements. The pH of the
primary aquifer also has a slightly acidic nature. These two variables can cause biofouling of the
screens by iron bacteria. However, with low abstraction rates the impact of this should be
insignificant.
COSTS
Where geological formations are favourable and the water table occurs close to the surface,
relatively inexpensive wellpoints can be constructed. By using jetting techniques contractors are
able to insert PVC casing up to depths of about 20 meters. Usually the cost of such an operation,
including the casing provided is in the range of R2000 to R2500. This compares well with the
comparative cost of drilling a 20 m deep borehole with air-percussion drilling, which would typically
be an order of magnitude more expensive. The cost of a centrifugal pump is about R 1000
(including connections and fittings). This means that a fully operational system can be installed for
under R 4000. This places it within the range of many households. Lower income households
however will generally not be willing to spend such an amount of capital towards garden irrigation.
The experience in Port Elizabeth, where different geological conditions exist and the cost of a
borehole is much higher, that private boreholes is almost exclusively found only in more affluent
neighbourhoods (Lomberg, et al., 1996).
ADVANTAGES AND DISADVANTAGES
As with every scheme there are advantages and disadvantages in using garden boreholes. These
are summarised in Table 2. The boreholes for garden irrigation would not require licensing but
would require some form of regulation by the relevant authorities. Large-scale abstraction in
coastal areas may cause salt-water intrusion, but this is unlikely due to the low abstraction rates
required for garden irrigation.
Table 2: The advantages and disadvantages of garden borehole use
Advantages Disadvantages
Savings in bulk water requirements Initial capital layout
Long term financial benefit Possible long term degradation of water
quality from possible saline intrusion
Devolution of maintenance from service
provider Possible soil subsidence
Job creation Possible impact on wetland systems
Research and development opportunities More groundwater quality protection and
pollution prevention required
Control water table fluctuations
The most common fear of groundwater abstraction in urban areas is that of land subsidence.
However, due to the natural groundwater level fluctuations this problem may not be very serious,
but will require additional monitoring and geotechnical research. Where abstraction is low the
water level stabilizes at a new equilibrium such that flow to the area of groundwater withdrawal
balances the abstraction (Foster et al., 1998). Irrigation return flow would also contribute to this
equilibration. The main concern would be the degradation of the water quality over time, with
pesticides, herbicides or through saline intrusion.
EDUCATION
Education and information dissemination should form an integral part of such a scheme. The main
focus would be on water conservation awareness as well using the garden boreholes responsibly.

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 338
Sensitising all role players on the importance of groundwater and the positive role it can play in
water conservation and demand management must play an important role. In Perth educational
units have been set up to run public campaigns in water resource education targeting schools and
the general public through ad campaigns (print and electronic media), competitions and
sponsorships.
The promotion of water wise gardening, including irrigation during periods of low
evapotranspiration (early mornings or just before or after sunset), drip irrigation and/or water
saving sprinkler systems, would help in preventing over exploitation of the Cape Flats aquifer.
CONCLUSIONS
The first step in encouraging widespread private garden irrigation would be through the building a
public awareness of the value of groundwater. The experience of Perth in public education could
provide water managers in Cape Town with insight on how to proceed with this. The use of private
garden boreholes will strengthen the city in its development of an integrated approach to water
resource management. It is envisaged that the use of private boreholes for garden irrigation will
form part of a larger education and water saving programme. Complimentary water saving
initiatives should also be encouraged such as rainwater harvesting and the installation of water
saving devices.
The idea of using groundwater resources is normally a progressive process that may take many
decades (Foster et al., 1998). Financial incentives for the installation of garden boreholes and
efficient water use may be required. Among the bigger challenges introduced by private garden
irrigation is the difficulty in exerting some degree of control over the large numbers of small-scale
abstractions.
If such an initiative is to work it will require the political and social will of the city’s managers and
the general public. The idea of using garden boreholes is attractive but will require more
investigation to determine its feasibility and affordability. It is recommended that a more
comprehensive study be launched to determine the feasibility of using garden boreholes for
irrigation
REFERENCES
Appleyard, S. J., Davidson, W. A., and Commander, D. P., 1999, The effects of urban
development on the utilization of groundwater resources in Perth, Western Australia, In:
Groundwater in the Urban Environment, Edited by Chilton, J., A.A. Balkema, Rotterdam, pp 97 –
104.
Department of Water Affairs and Forestry, undated, Water vir die Wes-Kaap. Pamphlet compiled
by Ninham Shand (Pty) Ltd.
Dorrington, R. E., 2000, Projections of the population of the Cape Metropolitan area 1996 – 2031,
Summary published on the City of Cape Town homepage:
http://www.capetown.gov.za/home/demographics.asp.
Forster, S; Lawrence, A and Morris, B. (1998) Groundwater in urban development. World
Technical Paper No. 390. The World Bank, Washington DC.
Fraser, L., and Weaver, J., 2000a, Cape Flats Aquifer: Bulk Water for Cape Town Now, Contract
Report submitted to Ninham Shand Consulting Engineers, Stellenbosch.

2nd WARFSA/WaterNet Symposium: Integrated Water Resources Management: Theory, Practice, Cases; Cape Town, 30-31 October 2001
The use of garden boreholes in Cape Town, South Africa: Lessons learnt from Perth, Western Australia 339
Fraser, L., and Weaver, J., 2000b, Groundwater Impact Scoping for the Cape Flats Aquifer,
Contract Report submitted to Ninham Shand Consulting Engineers, Stellenbosch.
Lomberg, C. R., and Roswarne, P. N., Raymer, D. A., and Devey, D. G., 1996, Research into
Groundwater Abstraction in the Port Elizabeth Miunicipal Area, Water Research Commission
Report, WRC Report No. 515/1/97.
Parsons, R., 2000, The role of Groundwater and its Impact on Urban Catchment Management,
The Thrid Bi Annual Symposium on Urban Catchment Management, 29 January 2000, Organised
by the Cape Metropolitan Council and the University of the Western Cape.
Sililo and Appleyard, in print, Shallow porous aquifers in Mediterranean Climates, In preparation for
UNESCO publication.
Statistics South Africa, 1996, Population Census, Pretoria.
Wicht, A. I., Meyburg, J. C., and Boustead, P. G., 1969, Rainfall at the Jonkershoek Forest
Hydrological research station, Annale Universiteit van Stellenbosch, Vol. 44, Serie A No.1. pp. 66.