Fixing leaks in water mains

Real losses or leaks account for a large portion of non-revenue water. In this article, we will look at the types of pipe leaks and strategies to reduce them.

Based on the IWA water balance, there are three types of real losses:

• leakage on transmission and distribution mains,
• leakage and overflows at utility storage tanks, and
• leakage on service connections up to the water meter.

Of course, every water supply network experiences some real losses. There is a minimum amount of water loss even in newly commissioned distribution systems, also called an unavoidable minimum. However, those losses should always remain within economic limits.

Many reasons may cause a water main leak, including: 

• Defective or improper valves, fittings, and pipe joints 
• Ageing/defective piping 
• Poor design/ inspection of the pipe network 
• Wrong construction practices 
• Vibration caused by traffic load 
• Ground and soil movement 
• Natural disasters such as flooding, earthquakes, etc. 
• Un- or mismarked water mains 
• Corrosion (internal or external) 
• Water hammer/pressure surges 
• Incorrect backfill.

A compromised pipe would often break, burst, crack, and split. Most of the main breaks utilities experience each year are due to failing pipes. While some leaks are small and will take a while to surface, others can be spotted immediately, causing significant damage and are more costly to mitigate. Let’s look at the most common types of pipe leaks and how to deal with them.

Water main breaks also referred to as pipe fractures, occur on water transmission lines. They represent catastrophic pipe failures, often resulting in loss of water pressure or service interruptions and sometimes severe damage to the surrounding infrastructure.

Water main breaks usually are relatively easy to locate, as a large amount of water released in these failures usually becomes quickly and visually apparent on the street level, especially in areas of high pressure. The causes of water main breaks are different: material decay due to corrosion, water hammer, damages caused by construction works, ground and soil movement, and natural disasters.

It is a misconception that main breaks, which are surfacing quickly and causing supply disruptions, are causing major water loss in the distribution system. At the same time, small hidden leaks and breaks may run for years and cause a much larger volume of real damage before repair. Despite relatively small water loss per the leak, these result in a significant total loss due to the numerous locations where leaks take place. Such kind of water loss is called background leakage and may be substantial while at the same time challenging to survey and repair.

Practice shows that most leaks occur at pipe joints and service connections. Pipe connections or flanges are leaking for various reasons:
 

• when the pipe is improperly supported (causing pipe movement),
• the ground movement has caused pipe joint separation,
• bolts are inconsistently tightened or loosened due to excessive pipe pressure,
• a rubber gasket is deteriorated or placed incorrectly,
• a joint/fitting is defective, or the body is corroded.

Water leaking from a compromised fitting may flow along the pipeline and can come to the surface far away from the source of the leak, creating enormous water losses before the leak is eventually found.

After a long period of inactivity, a valve can start leaking from a stem or a bonnet gasket. This is a common problem, particularly with old gate valves, where a packing gland starts leaking. However, a leakage can also appear in new gate valves, which have poor sealing or are produced from low-quality materials.

How to deal:

To avoid valve leakage, we recommend purchasing gate valves for potable water that conform to internationally accepted standards, such as EN 1074. Hawle manufactures gate valves with different connection options, such as flange, BAIO, System 2000 or PE sockets, and all of them ensure a reliable leak-proof connection for years. Learn more about how to select a gate valve. 

Pipe seepage would often occur on deteriorated asbestos cement (AC) pipes where the semi-porous pipe surface lets water through. Since the leak noise is minimal in the case of pipe seepage, such kind of leakage is challenging to locate.

How to deal:

One approach to minimize losses caused by seepage in AC pipes would be to reduce pressure in the pipeline. At the same time, it is worth mentioning that most of the AC water mains are approaching the end of their lifecycle and need replacement. In many countries, the use of new asbestos cement pipes has been banned for safety reasons, and most of the old AC pipes are being replaced by PVC or PE pipes.

Some studies suggest that service connection pipe leaks contribute the most to the annual real water losses of utilities. A standard service connection links the user with the distribution system and features multiple changes in pipe materials and diameters, resulting in an increased number of joints and fittings, which are more vulnerable to leaks. At the same time, service connections are often laid shallowly, close to the road surface. Traffic load causes movement and, therefore, weakens the pipe saddle, as well as valve joints. This creates numerous small background leakages, which can remain unreported for an extended period of time since the water would not come to the surface (unless a pipe bursts). It may take months and years until a service connection leak is repaired and add up to millions of litres of wasted water.

How to deal:

Service lines have the greatest number of leaks, running for longer periods undetected and unreported. The numbers are particularly high for the systems with high connection density and where the service line has reached its end of a lifecycle. For this reason, many water utilities have implemented a service line replacement program, which has proven its efficiency by curbing large volumes of water losses. Additionally, replacing service lines will reduce the new break frequency and, therefore, annual maintenance costs. 

To reduce the amount of non-revenue water from a service connection, we recommend using high-quality leak-proof valves and fittings. Hawle has developed a wide range of house connection solutions for any pipe and application, which have proved their efficiency with time.
 

Other leakages 

Other types of leaks include leakages from fire hydrants, air valves, and pumps. These are relatively easy to detect as they are usually visible or can be detected by direct sounding.