Planning to Review Your Water Distribution System
OWWA & OMWA Joint Conference, May 2004
By Ken G. Collicott, P.Eng.
1. INTRODUCTION
In the past, most Canadian municipalities focused on the capital works required to
support population growth with little consideration of the need to renew their distribution
system. However, in light of ageing infrastructure, public demands for a high level of
service and accountability, as well as more stringent legislation and competition for
limited financial resources, municipalities are now motivated to develop a plan for
renewal of their water distribution systems.
The framework for a water distribution system renewal plan can be described in terms
of seven questions.
- What do you have?
- What is it worth?
- What is its condition?
- What needs to be done?
- When do you need to do it?
- How much will it cost?
- How will you pay for it?
There are two complementary approaches to the development of a water distribution
system renewal plan: top-down and bottom-up. These two approaches differ in the
detail needed for preparation and how the results can be applied. The top-down
approach uses more readily available “system” data and is used for strategic long-term
planning of policies and programs, whereas the bottom-up approach looks at individual
assets and is used for short-term capital planning of projects. Short-term planning
typically covers a period of less than 10 years and long-term planning typically covers a
period of 10 to 100 years(1).
The magnitude of projected costs for renewal of a water distribution system over the long term can be quickly determined using the top-down approach. On the other hand, it may take several years to develop a comprehensive annual renewal plan for large systems using the bottom-up approach in light of the fact that a detailed inventory and condition assessment is required. Over time, the results of the bottom-up approach can be used to refine the top-down approach. 2. TOP-DOWN APPROACH
2.1 What do you have?
Even though a municipality may not have a detailed inventory of its water distribution
system, it should be possible to estimate the total length of water main and the number
of appurtenances using the following assumptions(2):
- total length of water main — typically 4 m to 6 m per capita;
- total number of hydrants — typically one hydrant for every 150 m to 250 m of
water main;
- total number of valves — typically one valve for every 100 m to 150 m of water
main;
- total number of water services — typically 0.2 to 0.3 services per capita; and
- total number of water meters — typically equal to the total number of water
services.
To compile a complete inventory of a water distribution system, municipalities should
also compile the rated capacity for each water treatment plant, well, pumping station,
and storage facility. This information is usually available from design reports, operations
and maintenance manuals, and permits.
2.2 What is it worth?
Several methods can be used to quantify the value of a water distribution system (e.g.,
original cost, depreciated cost, replacement cost). With the top-down approach, value
should be based on replacement cost. Unit costs for replacement of water distribution
system components can be estimated using input from other municipalities, local contractors, recent construction contracts, or technical reports (USEPA, 2001; NRC,
2002). The total replacement cost for a water system (including supply, treatment,
distribution storage and pumping) is typically $3,000 to $4,000 per capita(3).
2.3 What is its condition?
For the top-down approach, the age of the distribution system components can be used
as an indicator of condition. It should be recognized that age is not always a
good indicator of condition since there are many physical, environmental and
operational factors that can impact the rate of deterioration of distribution system
components. Ideally, the total length of water main should be broken down into
homogeneous groups (e.g. different combinations of pipe material and soil type) to
account for the different life expectancies of these groups.
If the year of construction for each water distribution system component is not readily
available, it would be reasonable to assume the distribution system expanded at about
the same rate as the population growth in the municipality. Historical population data
can be obtained from municipal records and Statistics Canada. The first year of
municipal water service should also be available from municipal archives. The year of
construction of buildings can also be used to estimate the age of the water mains along a
street.
2.4 What needs to be done?
Deteriorated mains can be replaced using open trench or trenchless techniques. Mains
can also be rehabilitated with structural linings if replacement is too costly or disruptive.
Internal corrosion of unlined iron water mains can cause water quality problems and
possible reductions in hydraulic capacity. These mains can be rehabilitated by nonstructural lining if they have not experienced high break rates. The feasibility of lining
and/or cathodically protecting a main depends on its structural condition and other local
factors.
Hydrants, valves, and water services are normally replaced within the road allowance
when the mains are replaced or rehabilitated. However, in some cases, it may be
necessary to replace these appurtenances before the main is replaced. The life
expectancy for hydrants, valves, and water services should be estimated based on local
factors.
2.5 When do you need to do it?
The service life of water distribution system components varies depending on several
factors, such as construction materials, quality of construction, soil conditions, water
quality, and level of maintenance. For the purposes of the top-down approach, a
service life can be assumed for each system component based on industry averages. As
a result, the remaining life of each component can be estimated by subtracting the age of
the component from its assumed service life.
To quantify the life cycle costs for a water distribution system, it is necessary to project
costs for each component over at least one life cycle. Since some components could
have a life cycle of several decades, costs are typically projected over a 100-year
planning horizon. Furthermore, life cycle costs are typically projected in 10-year
increments commensurate with the accuracy of the analysis.
The projected replacement costs can be calculated and graphed using an electronic
spreadsheet. A computer model can also be used to project replacement costs.
Examples include KANEW (AwwaRF, 1999), WARP (Rajani, B. and Kleiner, Y.,
2001), and Nessie (AwwaRF, 2001).
2.6 How much will it cost?
The projected costs for replacement of a water distribution system can be estimated by
summing the projected replacement cost for each system component. The projected
costs for rehabilitation of iron water mains can be estimated based on the total length of
iron mains to be rehabilitated and unit costs for non-structural lining. The timeframe for
rehabilitation of iron water mains will depend on available funding and the urgency of the
needs.
The long-term average annual cost for renewal of a water distribution system is typically
one to two percent of the total replacement cost (AwwaRF, 2001). This assumes the
average life expectancy of the water system components is 50 to 100 years. Since most
water systems in Canada experienced a significant growth rate in the 1950s and 1960s,
it is expected that renewal costs will increase significantly over the next few years as the
components that were installed during this period reach the end of their service life. The
resulting “hump” in costs, when graphed is sometimes referred to as the “Nessie Curve”
(AwwaRF, 2001).
2.7 How will you pay for it?
Municipalities should adopt the following principles when developing their water
distribution system renewal plan.
- Full cost recovery — all operating, maintenance, and capital renewal costs should
be recovered through water rates.
- User pay approach — directly charge water customers in proportion to the cost
of providing water service.
- Pay as you go approach — investment in renewal of a water distribution system
will have to be ongoing and, therefore, current revenue sources should be sufficient
to cover this ongoing cost. However, debenture financing is commonly needed for
large one-time capital expenditures (e.g., water treatment plant expansion) or large
emergency requirements.
It is important to project renewal costs over at least one life cycle for each component
so a financial plan can be developed that anticipates any projected increases in costs.
3. BOTTOM-UP APPROACH
Unlike the top-down approach that focuses on the long-term costs for renewal of a
group of assets, the bottom-up approach attempts to quantify the short-term costs for
renewal of each component in a distribution system. The bottom-up approach follows
the same framework as outlined above for the top-down approach.
The bottom-up approach should incorporate risk management principles where the
probability of failure and the consequences of failure are both considered in the
decision-making process. In the past, many municipalities have been prioritizing water
distribution system renewal plans to minimize capital costs without considering socioeconomic costs, such as traffic impacts, impacts on sensitive customers (e.g., hospitals), property damage, damage to other infrastructure, and loss of economic activity
(AwwaRF, 2000a).
3.1 What do you have?
The bottom-up approach requires a detailed inventory and condition assessment of
each component. Table 1 summarizes some of the physical data that should be included
in an inventory of water mains. All municipalities should compile the basic physical data.
Municipalities should also consider the need to compile some of the other advanced
physical data listed in Table 1 to facilitate the development of a renewal plan.
In light of the significant amount of data required to develop a comprehensive renewal
plan, municipalities should compile the inventory in electronic databases together with an
interface to a geographic information system (GIS). This inventory should be
coordinated with other applications, such as a maintenance management system.
TABLE 1 - CONDITION/PERFORMANCE INDICATORS
3.2 What is it worth?
Ideally, the cost data incorporated into the bottom-up approach should be sufficiently
accurate for capital budgeting purposes. If the inventory is compiled in an electronic
database, it is possible to develop “look-up tables” that include unit costs for
replacement of water mains, valves, hydrants, and water services. It should be clearly
indicated whether the unit costs include restoration, engineering, contingencies, and
taxes. The databases could also include cost multipliers to reflect the relative difficulty in
constructing water mains based on location (e.g., local road, arterial road) or
environmental conditions (e.g., high water table, difficult soil/rock conditions).
3.3 What is its condition?
Deterioration of water distribution systems can be described in terms of four general
categories: structural, hydraulic capacity, leakage, and water quality. Some physical,
environmental, and operational factors that contribute to water system deterioration are
identified in another best practice document, Deterioration and Inspection of Water
Distribution Systems (InfraGuide, 2002).
The best practice for investigating the condition of water distribution systems is based
on a two-phase approach. The first phase involves a preliminary assessment of the
potential problems using data that should be collected by every municipality on a routine
basis. The second phase involves a more detailed investigation of specific problems
based on findings of the preliminary assessment.
Valves and hydrants have a renewal approach and life cycle that is different from mains.
They should be routinely inspected and exercised to ensure they are accessible,
operable, conform to current design standards, and are not leaking. Valves and
hydrants that do not meet these requirements should be repaired or, if necessary,
replaced.
3.4 What needs to be done?
Figure 2 illustrates a flow chart for selection of alternative water main renewal
technologies. If a pipe does not conform to current design standards or is undersized,
then it should be replaced and is not a candidate for rehabilitation. Similarly, if a main is
in poor structural condition, then it is not a candidate for non-structural rehabilitation
(i.e., cleaning and lining).
FIGURE 2 – SELECTION OF ALTERNATIVE WATER MAIN RENEWAL
TECHNOLOGIES (Adapted from AwwaRF; 2002b).
It is also apparent from Figure 2 that there are several alternative renewal technologies
for each condition/performance indicator. Therefore, the most cost effective technology
should be selected on the basis of a life-cycle analysis that determines the lowest
present worth(4). The life cycle analysis should not only consider costs for infrastructure
repair, rehabilitation, and replacement, but also socio-economic costs.
A comprehensive water distribution plan will establish the following needs.
- Water mains and services that do not conform to current design standards in terms
of pipe diameter and/or material, depth of cover as well as water service diameter,
material and cover should be considered for replacement.
- Replace or structurally rehabilitate mains that have high break rates or leaky joints.
- Rehabilitate unlined iron mains with non-structural linings if they have not
experienced a high break rate, but their hydraulic capacity and/or water quality is
significantly affected by deterioration.
- Replace mains that are too small (even after being cleaned and lined) to supply the
required flows at adequate pressures.
- Cathodically protect metallic water mains, fittings and appurtenances if they are
installed in corrosive soils.
- Replace or rehabilitate highly critical mains before they fail.
- Repair or replace valves and hydrants that are non-standard, inoperable, or leaking.
Many factors will affect the selection of the most appropriate renewal technology for
each section of water mains. It should be noted that some renewal technologies are not
available locally. It should also be noted that due to the high mobilization costs of some
rehabilitation technologies, they are only cost effective when a significant quantity of
water main is to be rehabilitated.
3.5 When do you need to do it?
Economic analyses should be undertaken to determine the most efficient timing for the
following.
- Is it more cost effective to replace or structurally rehabilitate a main rather than
continue to repair it?
- If the soil is corrosive, is it cost effective to cathodically protect a metallic water
main and/or other metallic components (e.g. valves, hydrants, fittings) to extend their
life?
- Is it more cost effective to rehabilitate an unlined iron main rather than continue to
pay higher pumping costs and/or construct additional mains to provide the required
hydraulic capacity?
- Is it more cost effective to rehabilitate leaky joints in large diameter mains rather
than continue to lose water?
- Is it more cost effective to co-ordinate the work with other projects (e.g. road
reconstruction, sewer replacement) to achieve synergistic benefits?
If the rate of deterioration can be estimated, then it is possible to predict the timing for
renewal of water mains using a cost–benefit analysis. The timing for renewal of water
mains that experience high break rates, leaky joints, and reduced hydraulic capacity is
primarily dictated by economics. However, the timing for renewal of water mains that
do not conform to current design standards or impair water quality is dictated by the
severity of the problem and the available funding.
To minimize costs and disruption, the proposed water main renewal program should be
coordinated with sewer and road reconstruction projects as well as upgrades that might
be required for new development/redevelopment. In addition, the individual sections of
water main to be renewed should be grouped according to geographic area to minimize
cost and disruption.
Once the need for renewal of a water main has been established, municipalities should
use a condition rating system to assist with prioritizing a renewal program. Several
factors can be used to quantify the condition or performance of a water main in terms of
structural condition, hydraulic capacity, leakage, and water quality. The condition rating
systems should also incorporate information on the importance and hazard potential of
each water main. The number of factors to be included in a condition rating system will
vary amongst municipalities depending on the size of the municipality, the data available
and the specific conditions within each system. Large municipalities should consider the
need for a computerized decision support system to facilitate renewal planning.
3.6 How much will it cost?
The projected renewal costs for water distribution system components can be estimated
using input from other municipalities, local contractors, recent construction contracts,
and technical reports (USEPA, 2001; NRC, 2002). It should be noted that cost
estimates for some renewal technologies are very site specific. The projected renewal
costs should be compared with those estimated using the top-down approach to ensure
the short-term plan is consistent with the long-term plan.
3.7 How will you pay for it?
User rates are the preferred source of revenue for renewal to ensure a stable and
adequate level of funding is available and to promote efficient use of the resources. In
some cases, municipalities have added a surcharge to the water bills to generate added
revenues to cover the cost for renewal of the distribution system (e.g., cast iron
replacement programs) and to enhance awareness for the need for such programs.
Since water distribution system renewal programs are ongoing and the investment
requirements do not change radically year to year, the use of current funds is preferred.
Municipalities should track the renewal costs for their water distribution system
separately in their capital budget to ensure spending is sufficient and efficient.
Affordability is the concept of ability to pay, as opposed to willingness to pay, to which
decision makers are more sensitive. Affordability is often evaluated by expressing water
charges as a percentage of median household income (MHI). The U.S. Environmental
Protection Agency provides information on drinking water affordability (EPA, 1997)
with affordable water generally considered being one to two percent of the MHI. A
British study (Sawkins, J.W. and Dickie, V.A, 2002) cited a benchmark affordability
level for water plus sewage charges of three percent of MHI. The 2000 median
Canadian family income was $51,000 (Statistics Canada, 2002), which at 1.5 percent
would mean an annual water bill of $765 should be affordable, on average. Of course,
local conditions will vary.
Sometimes, water costs are compared with other services to encourage approval of
higher rates. Often, water plus sewer costs are in the same range as cable or satellite
TV services, which many find affordable.
4. CONCLUSIONS
All municipalities across Canada should be using both the top-down and bottom-up
approaches for developing a water distribution system renewal plan. These approaches
must be tailored for each municipality to reflect the size and age (i.e. condition) of their
system. In some cases, particularly small municipalities where in-house expertise in
renewal planning is not present, it may be necessary to retain a qualified engineering
consultant to assist with the development of renewal plans.
ACKNOWLEDGEMENTS
This paper is based on a “best practice” report published by the National Guide to
Sustainable Municipal Infrastructure (InfraGuide). A complete copy of the report can
be downloaded from www.infraguide.gc.ca.
FOOTNOTES
- This paper is based on the Best Practice developed by the InfraGuide and facilitated by R.V. Anderson Associates Limited.
- Based on studies conducted by R.V. Anderson Associates Limited for seven Canadian
municipalities with populations ranging from 50,000 to 500,000.
- Based on studies conducted by R.V. Anderson Associates Limited for seven Canadian
municipalities with populations ranging from 50,000 to 500,000.
- Present worth analysis is a technique used to compare alternative schemes that have different
costs over a certain planning period. The present worth represents the current investment that
would have to be made at a specific discount (or interest) rate to pay for the initial and future cost
of the works.
REFERENCES
AWWARF (American Water Works Association Research Foundation), 1999.
Quantifying Future Rehabilitation and Replacement Needs of Water Mains.
———, 2001. Financial and Economic Optimization of Water Main Replacement Programs.
———, 2002a. Cost of Infrastructure Failure.
———, 2002b. Decision Support System for Distribution System Piping Renewal.
Canada, Statistics Canada, 2002. The Daily, July 18, 2002.
InfraGuide (National Guide to Sustainable Municipal Infrastructure), 2002.
Deterioration and Inspection of Water Distribution Systems.
———, 2003. Selection of Technologies for the Rehabilitation and Replacement of a Water Distribution System.
NRC (National Research Council Canada), 2002. Construction and Rehabilitation Costs for Buried Pipe with a Focus on Trenchless Technologies.
Rajani, B. and Y. Kleiner, 2001. WARP – Water Main Renewal Planner.
Proceedings of the International Conference on Underground Infrastructure Research, Kitchener, Ontario, June 11-13, 2001.
Sawkins, J.W. and Dickie, V.A., 2002. Affordability of Water and Sewerage Services in Great Britain.
United States, EPA (Environmental Protection Agency), 1997. Information on Developing Affordability Criteria for Drinking Water.
———, 2001. 1999 Drinking Water Infrastructure Needs Survey – Modeling the Cost of Infrastructure.
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