Each source of existing and planned water supply should be identified and quantified. Descriptions should also be provided of the water treatment that will be required to make the water potable. In addition, this is an important exercise in defining capacities and costs of existing and planned water and wastewater facilities, including both capital costs and operation and maintenance costs.
Sources of water supply are typically broken down as:
• Surface water
• Groundwater
• Recycled/reclaimed water
• Desalination water
• Other (rainwater harvesting and graywater systems).
3.4.1 Surface water
Where the source of supply is a surface water reservoir, analysing usable storage capacity and historical storage volumes will enable the available water supply to be assessed. Records of treatment plant production based on readings from production meters, if available, will provide data on historical water production. Design criteria for treatment plants can be used to assess unutilized capacity available for accommodating future growth.
If the source of water supply is a river, available information on stream depth from stream gauges converted to flows may be useful in quantifying variations in historical stream flows. If the water intake is unmetered then the water volume used can be estimated from pump characteristics and periodic electricity meter readings. The latter will indicate the period that the pump was running. The pump curve (available from the manufacturer) will indicate what flow was pumped, based on the pumping head for the installation.
New sources from surface water supplies, reservoirs or river diversions, should be identified in terms of production capacity and total capital construction costs as well as operation and maintenance costs, as such projects could be deferred or downsized due to the water demand management programme.
BOX 3.1 (Continued)
Key findings from both assessments were similar as follows:
(1) There is a general gap in local expertise, technology, and approach to better understand how climate change could affect water services delivery in urban centers and to plan for addressing climate change impacts and building adaptive capacities;
(2) Continued advocacy and engagement of various stakeholders – including the academic community, local and national government, policymakers, and communities–are critical to raise awareness of climate change and its impacts;
(3) Limited or lack of climate-related data, and associated know-how to distill useful information from those data, restrict water services providers from fully comprehending how climate change may impact their operations and sustainability of services delivery; and
(4) Learning from peers or other practitioners that have undertaken activities to become climate resilient is an ideal capacity building approach to plan and take action for addressing climate change impacts.
Source: WaterLinks (2013a).
3.4.2 Groundwater
In the case of groundwater sources, the sustainability of available water supplies is directly related to the amount of water entering the groundwater basin as recharge compared to pumping rates. A reduction of overdraft (i.e., when groundwater pumping exceeds groundwater recharge) that extends the life of the groundwater supply source should be counted as a benefit from the demand management programme.
This also provides an important exercise in defining capacities as well as costs of existing and planned water and wastewater facilities (including capital costs and operation and maintenance costs).
Recharge rates are typically quantified using peizometers adjacent to the pumping zone of supply wells. Alternatively, if a conjunctive water-use scheme is in place, where groundwater is mostly used in the high irrigation (dry) season when surface water flows are lower, it must be allowed to recharge aquifers during the wet (monsoon) season when higher surface water flows are used for irrigation.
Recharge rates can be estimated by measuring water levels in supply wells during the low irrigation (less groundwater pumping) season.
Plans for new groundwater wells to increase supply capacity should include production capacity, capital costs, and operations and maintenance costs.
3.4.3 Recycled water and desalination
Access to seawater for desalination may be considered, if applicable. Existing or planned facilities for treating wastewater or seawater should be identified in terms of treatment capacity as well as capital for improvement, and operations and maintenance costs. Practically speaking, both recycled and desalinated water supplies are reliable sources of supply that are sustainable but they are very expensive (as much as 10 times more expensive on a volumetric (per cubic metre) basis than conserved water). These sources are easily quantified from designed capacity and metered production at treatment facilities. An example of treating and reusing wastewater as a source of water in is described in Case Study 3.
3.4.4 Other sources
In some cases, where water supplies are too low in pressure, unavailable on a day-to-day basis or are of poor quality, supplies are delivered by tanker trucks to supplement water utility output. Tanker truck records, interviews with operating personnel and community surveys can be used for quantification purposes.
Quantifying on-site graywater use and rainwater harvesting by specific customers requires a survey of water customers or another reporting mechanism, such as the number of systems sold or provided by the utility. Assumptions are commonly made on this aspect in cost-effectiveness analyses as this relatively small quantity of water provides relatively low cost savings. The exception to such assumptions is when local knowledge of the service area indicates participation by numerous customers in these activities, such as in some parts of rural Australia where over half of the water supply is provided by rainwater harvesting. Water savings from demand management measures are discussed in more detail in Chapter 6.
Availability of other supply sources, such as stored and treated urban storm water, varies due to local climatic conditions and water system designs. Quantified amounts and cost information are usually available from utility engineering departments.
3.4.5 Water sources quality
Quality problems need to be identified as they can have a major impact on the amount of supply produced as well as cause shifts in water management schemes. Particularly important are water quality variations that
limit availability of water of suitable quality to meet peak demands. The treatment requirements for producing potable water from different sources should be noted. A useful reference could be a list of water quality‘constituents of concern’that are monitored and treated.1
Groundwater contamination due to natural or man-made causes, whether potential or existing, should be noted. If groundwater treatment is planned or required due to water quality concerns, details should be given of capacity, capital and operation and maintenance costs for new groundwater treatment facilities. Also of concern is the level of treatment provided for recycled or desalinated water as well as restrictions on its uses. If these sources are non-potable and used only for irrigation purposes, this should be taken into account as a factor in reducing peak demand for treated water during the irrigation season.
3.4.6 Water transfers
/////exchanges
Existing or planned agreements for meeting demands through (raw and/or treated) water exchanges or transfers under normal supply conditions or only in dry years on a short-term basis may form an important supplement to local sources. Water transfers can work both ways. In some cases, providers become suppliers to other agencies during dry periods, which count as an additional demand on the system. In other cases, providers receive water from other providers and that counts as additional supply.
The provisions of these agreements should be understood as well as the cost of water supplied to, or received from, other providers.
Box 3.2 describes Singapore’s experience in creating new sources of water.
BOX 3.2 SINGAPORE’S EXPERIENCE IN WATER MANAGEMENT Approximately two thirds of Singapore’s land area
is used as water catchments. All major traditional surface water resources have been developed.
Singapore has more than 1 million water accounts.
PUB, Singapore’s national water agency, adopts a holistic and integrated approach in water management, from sourcing to the collection, purification and supply of drinking water, to the
treatment of used water and its reclamation into ultra-clean, high-grade reclaimed water called NEWater, as well as the drainage of stormwater. To ensure an adequate and sustainable supply of water for Singapore, PUB has developed a diversified water supply strategy known as the Four National Taps. These are namely local catchment water, imported water from Malaysia, NEWater and desalinated water. Today, NEWater and desalinated water can meet 30% and 10% of Singapore’s total water demand respectively. Additional information is available at http://www.pub.
gov.sg
1An example of the constituents list that is maintained in the United States by the Environmental Protection Agency (USEPA) can be found at http://www.epa.gov. Water quality information, including drinking water testing requirements, can be found at http://water.
epa.gov/drink/contaminants/index.cfm and in the publication,Standard Methods for the Examination of Water and Wastewater, 22nd Edition, 2012, American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF), http://www.apha.org/media/
3.4.7 Water Treatment and Distribution System
The following aspects should be discussed:• The capacity and conditions for, and costs of, maintaining an existing conveyance, treatment and distribution system in terms of system components’age, pumping energy and treatment chemicals required;
• Type of water supply delivery (piped, by truck, others);
• Routine operation and maintenance, the pipe replacement schedule, and the history of main breaks and leak repairs.
In addition, the system pressure should be documented. These are key data for assessing the quantity of treated water that will actually meet customer demand. If leakage reduction programmes, pressure management or other demand management measures are not in place, water conveyance and distribution losses may be viewed as limiting the water source supply.