WDNs are a critical component of modern potable water production, treatment and distribution systems. Their importance lies in ensuring that water reaches consumers efficiently, meeting quality standards and keeping water losses within acceptable limits. However, WDNs face significant challenges, such as physical deterioration of pipes, which leads to water losses, service interruptions and higher maintenance costs. WDNs account for up to 80% of total maintenance and repair expenditures in drinking water systems (Kleiner & Rajani, 2001). In addition, the reactive approach to failure management increases operating costs and limits proactive planning, underscoring the need for optimal design and maintenance of these systems.
Subsystem: Pipelines
Within the WDN are valves, gates, sensors, however, pipelines are the largest and most complex subsystem, so their optimal design is of vital importance. The American Water Works Association (AWWA) has established rigorous standards to ensure that the materials used in the manufacture of pipes do not contaminate drinking water. One of the most relevant standards is ANSI/NSF Standard 61, which ensures that materials in contact with water are safe for human consumption.
In addition to complying with these standards, pipe design must consider key aspects such as:
• Mechanical strength: Ability to withstand internal pressures and external loads, such as vehicular traffic.
• Durability: Ability to operate for decades without significant failure.
• Corrosion resistance: Both internal (from water) and external (from the soil in which they are buried).
• Water quality: The pipe material should not alter the properties of the water.
• Ease of repair and maintenance: Pipes should allow easy connections and repairs.
Piping Systems
Piping systems are divided into three main categories:
1. Transmission Lines: large diameter pipelines designed to transport large volumes of water over long distances. These pipelines are crucial to protect the quantity and quality of the water resource, as well as to maintain infrastructure investment and avoid supply interruptions.
2. Distribution Mains: Pipelines that transport water from transmission lines to consumers.
Service Lines: Small diameter pipes that connect the distribution mains to the final consumption points.
In this study, the design of pipes for transmission lines was evaluated, due to their importance in the transport of large volumes of water and their impact on the continuous supply to the population. The three most used pipes in practice were selected:
Option (1) Ductile Iron Pipe, (2) Steel Pipe and (3) Concrete Pipe. These materials were evaluated in terms of: energy required to produce 1 linear meter of pipe and emissions of pollutants generated during it production, such as CO2, NOx and SO2.
Figure 1. Water Pipe design options. (1) Ductile iron, (2) steel and (3) concrete.
Life Cycle Timeline
The Life Cycle Timelines for each of the design options are presented in the following figures. According to studies, the average useful life of a pipeline network is approximately 50 years, considering the necessary maintenance activities according to the type of pipe installed. These interventions are essential to guarantee the continuous and efficient operation of the system.
Maintenance activities vary according to the selected design option. For example:
• For Ductile Iron and Steel Pipe pipes, interventions are mainly focused on repairing internal and external corrosion, as these materials are more susceptible to this type of deterioration.
• For Concrete Pipe, priority activities include break inspection and crack repair, due to the nature of the material.
There are common activities for all three design options:
1. Joint leakage inspection: This activity should be performed every 5 years in all cases, since joint leaks are one of the main causes of water loss and reduced system efficiency.
2. Internal inspection and cleaning: The objective is to keep the internal roughness of the pipe as low as possible, avoiding clogging and ensuring that water quality is not affected. For Concrete Pipe, this activity should be performed more frequently (every 5 years), while for Ductile Iron and Steel Pipe, the frequency may be less.
These interventions are essential to prolong the useful life of the pipes, minimize water losses and guarantee a continuous and quality supply to the population. Proper planning of these activities helps to reduce operating costs and avoid service interruptions.
Figure 2. Life Cycle Timeline for design options. (1) Ductile Iron, (2) Steel and (3) Concrete.
Life Cycle Inventory and Cost Analysis
The results obtained indicate that the production of ductile iron pipes requires almost five times more energy than the other two design alternatives. In addition, it generates a higher amount of pollutant emissions.
On the other hand, concrete pipe manufacturing consumes significantly less energy and emits slightly less CO₂ compared to steel pipes. However, in terms of other pollutants, steel pipe production is more environmentally friendly.
To make a better decision, it is essential to apply the Analytic Hierarchy Process (AHP) methodology, allowing to comprehensively evaluate the environmental impacts and costs associated with each option.
Figure 3. Results of total energy consumption and contaminants emissions for each design option. (1) Ductile Iron, (2) Steel and (3) Concrete.
Multi-Criteria Decision Making (AHP)
The results of the analysis using the AHP method are presented in Figure 4, where it can be seen that the Steel Pipe design option obtains the highest score with 48.3%, followed by Concrete Pipe with 42.1%, and in last place Ductile Iron, with only 9.6%. This low percentage is mainly due to its high energy consumption in production and its high levels of pollutant emissions compared to the other options, making it the least favorable alternative from an environmental and energy efficiency perspective.
According to these results, Steel Pipe is the best rated option under the energy consumption and emissions criteria. However, it is important to note that these results may vary depending on the approach taken in the analysis.
Figure 4. Multi Criteria Decision Making analysis results comparing each design option. (1) Ductile Iron, (2) Steel and (3) Concrete
To achieve a more complete evaluation, it would be essential to complement this environmental approach with an analysis based on operability, considering technical aspects and quality standards, such as ANSI/NSF Standard 61. This standard evaluates key characteristics of pipelines, such as strength, durability, corrosion protection, smoothness of the internal surface, pressure capacity, and maintenance of water quality, among others.
By integrating both environmental and technical-operational approaches, more conclusive results could be obtained and better inform decision making.
References
[1] ANSI/NSF. (2020). NSF/ANSI Standard 61: Drinking Water System Components – Health Effects. NSF International.
[2] Kleiner, Y., & Rajani, B. (2001). Comprehensive Review of Structural Deterioration of Water Mains: Statistical Models. Urban Water Journal, 3, 131-150.
[3] Sempewo, J. I., & Kyokaali, L. (2016). Prediction of the Future Condition of a Water Distribution Network Using a Markov-Based Approach: A Case Study of Kampala Water. Procedia Engineering, 154, 374-383.
Steel Liquid Storage Tank | Water Distribution Network | Dam | Primary Sedimentation Tank/Wastewater Treatment