10 20 Time [d]
Chapter 6 Use of LCA in planning water and sanitation infrastructure
6.2. Base case
Inanda dam
52 52
2 657 kg
0 5.llE-02kg/kL V
Wiggins Waterworks
52 52
11 388 kg
0 2.19E-01kg/kL
\>
Distribution
52 40
7 228 kg 1
30%
1.39E-01kg/kL
'
Consumers
40 24
'
40%
'
Collection
24 24
3 600 kg 1
0 l.50E-02kg/kL
'
Primary treatment
24 24
2 688 1
0 1.12E-01kg/kL
'
Sea disposal
24 24 0
Legend:
Unit Name Flow in
(MLVdav
Flow out (MlVday) Total C 02 load (kgC02equiv.)
% losses Specific CO2 load (kg C02/kL)
Figure 6-4: Simplified flowsheet of the base case.
The environmental impacts of the base case are presented graphically in Figure 6-5.
Primary treatment, 2736
Collection, 3 6 0 0 / ^ B
Distribution, 7 2 2 8 N .
Inanda dam, 2657
/ \
J Wiggins, 11388
Figure 6-5: Global warming impact for the Base Case for the supply of water and sanitation services to 200 000 households per day (in kg C02 equivalents).
Table 6-2 shows how a total burden for the entire system was calculated.
Table 6-2: Breakdown of the global warming impact of providing 200 000 consumers in the eThekwini Municipality with water and sanitation using the units from the base case.
Unit
Inanda dam Wiggins waterworks Distribution Collection Primary treatment Total
Vol produced (ML)
52 52 52 24 24
Impact per kL (kg) 5.11E-02 2.19E-01 1.39E-01 1.50E-01 1.12E-01
Total Impact (kg) 2657 11388
7228 3600 2736 27609
The sources of the impacts from the base case have already been examined in the interpretation and improvement analysis of Chapter 3. However it is important to ask whether the system as a whole is being managed efficiently and if not, could not an environmental improvement be achieved by better management practice.
At present approximately 30 percent of the 280 000 Ml purchased annually is unaccounted for within the ETM. Table 6-3 provides a detailed breakdown of the way water is used in the ETM.
One of the important facts that the table shows is that 232 Ml / d of water are unaccounted. Of
this 62 ML/d is from illegal connections and 170 ML/d from leaks. Because of this relatively high loss of water, a Non Revenue Water (NRW) branch has been established to reduce the amount of unaccounted for water.
Table 6-3: Breakdown of the supply and use of water within the eThekwini municipality (source Bailey, 2003)
Description
Amount of bulk water purchased (kl) Treated water supplied to:-
Residential - full pressure water Residential - semi pressure Residential - groundtank / standpipe Non Domestic
Others
Subtotal treated water supplied Untreated water supplied Total water supplied
Difference -> Purchase - Sales
Reticulation leaks, Reservoir Overflows, Service connection leaks Illegal Connections
Total water loss
July 2002 to June 2003
(kl) 274901152
104479534 3497936 4008635 77998590
189984695
189984695 84916457 62413596 22502861 84916457
% of total
54.99%
1.84%
2.11%
41.06%
100.00%
3 1 % 74%
26%
Consumers connected to illegal connections will be incorporated into the billing network of the municipality. This will not reduce the total water demand, however according the ETM's Integrated Development Plan (IDP) there is a 5 year goal of reducing the amount of illegal connections by 60%.
A reduction in water demand can be achieved by correcting the leaks. In 2003 the Inefficiency of Use (IOU) percentage was 30,4%) and the Infrastructure Leakage Index (ILI) was 8.1. An ILI of
1 is equivalent to achieving the least possible water with regard to pressure, length of mains and number of connections. Plans are currently in place to lower the ILI to 5 in the medium term (IOU 25%) and in the long term an ILI of 3 (IOU 20%) should be achievable.
Some of the measures to be introduced are;
• Active Leakage Control -Leak detection is to be typically done in discrete areas where a base line has been obtained.
• Water Wizard - a GIS based utility, which enables monthly water balances to be carried out in areas where the bulk meters exist.
• High consumption customers are short-listed and contracted plumbers are instructed to investigate and leave an "offer to repair" letter. If consumption does not drop, the property is visited again after 3 months. If consumption does not drop and arrears are in excess of 60 d, a forced repair is done and charged to the consumer.
For large reticulation networks approximately 10% of water is lost through leaks which cannot be economically repaired (Bailey, 2003). A Swedish project investigating the environmental sustainability of urban systems stated that for a well functioning network a 15% leakage rate was acceptable (Lundin, 1999). If the ETMs measures are successful and even a 20% IOU is achieved an additional 150 Ml/d would be released for use by potential new customers.
Another way of increasing the available supply of water is to reduce the demand. This method called least cost planning (LCP) has emerged as the way forward for water utilities in regions where water conservation has become an objective or where ongoing supply expansion is constrained (Fane, 2004).
Least cost planning originated in the energy sector in the United States during the 1980s for comparing energy conservation programs to increased generation as sources of supply. It was based on the realisation that a kilowatt of electricity saved through demand management was the equivalent of an increased amount of supply (Beecher, 1996).
There are many ways of reducing the water demand in a large city and these fall into two broad categories. Consumer demand and supplier demand. In the case of Durban the eThekwini Municipality is the supplier and the inhabitants of Durban the consumers. Consumer demand can be reduced by using measures such as installing low flow showerheads, low flush toilets or by using legislation which introduces water restrictions such as preventing the watering of gardens during the day. Supplier demand can be reduced by identifying and reducing leakages in the reticulation network, removing illegal connections and reducing excess pressure across the distribution system to reduce leakages.
Bailey, in his study on using water supply tariffs as a water management tool, found that for the ETM, one of the easiest ways of reducing consumer demand would be to introduce a new tariff structure which would reward the use of less water and penalise heavy users of water.
Using Ramsey pricing principles a pro-poor tariff structure was designed for the ETM. This tariff structure ensures that the poor have access to affordable water services while the rich pay a premium to cross subsidise the consumption of the lower groups. In keeping with the national government policy, the first 6 kL per month of water is free to all households.
Bailey showed that by using this tariff structure an average reduction of 3.3 percent in consumer demand could be achieved. This is due to reductions in consumption from not only the high users of water but all users. Lower income users reduce their demand in order to stay below the 6 kL per month limit and thus not pay for water at all while middle and high income users reduce there demand to avoid being heavily penalised for using more than 27 kL per month.
The ETM currently supplies 753 Ml per day. A 3.3 percent reduction in demand would translate into almost 25 Ml per day being freed up for use by new customers.
Another benefit of demand management is a reduction in electrical use. Lundie (2002) found that by using demand management the energy requirement for a system could be reduced by 4%
coupling this with energy efficiency measures could reduce the electricity demand by a further 9%. This would translate to a similar environmental benefit for this case due to the high electrical demand for the collection of sewage.