Controlling flow and pressure in water networks: the keys to sustainable performance

With its wealth of knowledge and expertise, the Claire Group works alongside industry players every day to achieve this goal. By providing reliable and robust equipment, as well as advanced monitoring and control solutions, it helps improve network performance and reduce losses.

There are two crucial physical parameters at the heart of this optimised management approach: flow rate and pressure. It is essential to be able to measure, understand and control this data in order to distribute water efficiently, minimise losses and guarantee a high-quality water supply. For example, excessive pressure can weaken pipes and cause them to burst, whereas a poorly controlled flow rate can lead to imbalances or interruptions in supply.

By combining technologies and real-world expertise, network managers can respond to today’s challenges while anticipating those of tomorrow. And this is precisely the approach taken by the Claire Group: offering solutions to manage water networks in ways that are increasingly intelligent, sustainable and responsible.

To be able to manage a drinking water network effectively, it is essential to begin by understanding what flow rate is. To explain it simply, flow rate (often denoted by Q) represents the amount of water that flows through a section of pipe over a given period of time. In other words, it is the volume of water that passes per unit of time.

In the industry, it is generally expressed in litres per second (L/s) or cubic metres per hour (m³/h), which are units that can be used to assess both small domestic flows and large industrial or collective flows.

So how do we determine this flow rate? It depends on two main parameters:
The velocity (V) at which water flows through the pipe.
The cross-sectional area (A), i.e. the internal surface area of the pipe through which the water flows.

The relationship between these parameters is straightforward:
Flow rate (Q) = Velocity (V) × Cross-sectional area (A).

An essential principle of physics to remember: the flow rate remains constant along the entire length of the pipe (in the absence of leaks, of course). This means that if the section of the pipe narrows at a given point (for example, if it goes from a wide pipe to a narrower pipe) the velocity of the water must automatically increase for the same amount of water to continue flowing over the same period of time.

This phenomenon can be directly observed in networks: in areas where diameters are reduced, variations in parameters, if they are not controlled, can weaken installations. This is why a clear understanding and effective monitoring of flow rates are essential factors to optimise network performance, prevent losses and maintain reliable distribution.

In an urban network, flow rates of several hundred m³/h can be reached at the entry point to a neighbourhood, whereas at the level of an individual household, the flow rate is more likely to be between 0.1 and 0.5 L/s (Source: Water Information Centre, 2023).

In contrast, pumps are capable of generating much higher flow rates, reaching thousands of m³/h. When it comes to velocity, it is generally recommended that it be around 1 m/s (or 3.6 km/h) in pipes, with a permitted minimum of 0.5 m/s (or 1.8 km/s).

Understanding this relationship between flow rate, velocity and pipe diameter is fundamental when designing and operating an efficient network. For example, to achieve a flow rate of 4 m³/h at a velocity of 1 m/s, a pipe with a minimum internal diameter of 37 mm would be required. The sources provide detailed tables showing the theoretical maximum flow rates for different sizes of copper pipes at speeds of 1.5 m/s and 2.0 m/s.

How can the flow rate of a water network be measured?

Measuring the flow rate in a drinking water network is not just a technical exercise: it is a key step towards accurately assessing consumption, detecting invisible leaks, optimising distribution and, ultimately, safeguarding efficient and sustainable management of resources. To achieve this, several meter technologies exist, with each one suited to specific uses and conditions.

However, keep in mind that selecting a meter does not depend solely on the diameter of the pipe, as one might think, but rather on the range of flow rates that are expected to be measured. In other words, it is important to know:
- The peak flow rate (when the installation is under intense use),
- The mean permanent flow rate (the most common on a daily basis),
- The minimum flow rate (when consumption is very low or even virtually zero).

These values must be compared with the characteristic flow rates defined by the manufacturer for each meter:

Minimum flow rate (Q1): the lowest flow rate at which the meter remains reliable and accurate, with a maximum error margin of ± 5% tolerated.

Transitional flow rate (Q2): the pivot point between the low accuracy zone (Q1–Q2) and the high zone. It must adhere to a maximum error of ± 2%.

Permanent flow rate (Q3): the maximum flow rate that the meter can withstand continuously without fatigue or abnormal wear. It corresponds to normal use, i.e. under conditions with constant or intermittent flow rates.

Overload flow rate (Q4): the maximum flow rate that the meter can handle at any given moment without sustaining damage.

To guarantee high quality and performance, European regulations (in particular European Standard MID 2014/32/EU (MID) of 26/02/2014) stipulate that a good meter must display a Q3/Q1 ratio of at least 10, meaning that its permanent flow rate must be at least ten times higher than its minimum flow rate. For example, if a meter has a Q1 of 0.16 m³/h, it must be able to handle a Q3 of at least 1.6 m³/h.

According to industry data, approximately 35 million meters are currently in use in France (Source: Observatoire national des services d’eau [France’s national water services observatory], 2023), and the gradual transition to smart meters is paving the way for even more accurate, real-time monitoring, which will make it easier to detect anomalies and excessive consumption early on.

Measuring technologies include volumetric piston meters and velocity meters such as turbine meters or Woltmann meters (with axial or floating impellers). Remote meter reading, which involves using pulse or encoder meters, now represents a significant step forward in monitoring water consumption. In addition to being able to view data in real time, it can also be used to quickly identify anomalies or leaks, thereby preventing losses that are often invisible to the naked eye. This system is a powerful lever for optimising water networks. According to France’s national water services observatory, local authorities equipped with remote meter reading technology can reduce losses by up to 20% on average (Source: ONSEA, 2023).

Positioning: meters are generally placed on a horizontal pipe, although some models can be adapted for vertical installation.
Environment: avoid installing them under equipment that may leak (to prevent them from becoming submerged) and protect them carefully against frost, especially in exposed areas.
Avoid high points: installing a meter at the top of a pipe can cause degassing, which can interfere with the measurements.
Accessibility: the chosen location must be easily accessible for maintenance, servicing or dismantling operations.
Respect the direction of flow: this may seem obvious, but it is a crucial step: if incorrectly oriented, the meter will not work properly.
Straight pipe lengths: for turbine or impeller meters, it is essential to have sufficient straight pipe lengths upstream and downstream, or, failing that, to use flow stabilisers to ensure measurements are reliable.
Prepare the network: before installation, it is recommended to flush the pipes thoroughly to remove any particles that could damage the device.
Commissioning: it is essential to open the valves gradually (upstream first, then downstream) to avoid any hydraulic shock when flooding the system.

Accessories are often necessary for a correct and long-lasting installation: an upstream filter (required for Woltmann meters), shut-off valves for dismantling, reducer tapers if the pipe diameter differs, a drain valve, and a downstream non-return check valve. In terms of maintenance, an annual check is recommended, and for Woltmann meters, periodic cleaning of the straight sections and calibration approximately every 5 years is recommended.

All metering solutions and accessories can be found in the Claire Group’s Drinking Water Supply catalogue.

Claire Connect delivers innovative solutions for flow measurement. The BLUE logger, the latest IoT innovation, is ideal for this task. It has inputs for pulse counting (up to 100 Hz), which can be used with meter transmitter heads. It can also be connected to electromagnetic flow meters via Modbus (compatible with brands such as Krohne, ABB and Siemens). Thanks to this versatility, it is possible to measure flow rates and transit volumes, which is essential data for sectorisation.

Water pressure, in simple terms, is the force exerted by water on the walls of the pipe that contains it. This force is primarily generated by the weight of the water column overhead. To visualise this easily, imagine a water tower: the higher the tank, the greater the pressure at the base. In other words, water height is a critical parameter that determines the pressure available in the drinking water network.

However, it is important to note that this pressure is not uniform across the entire network. It gradually decreases as the water moves away from the starting point, such as the water tower. Why? Due to pressure losses. These losses are caused by several factors: the length of the pipes, their condition (e.g. whether there is any limescale or deposits), the presence of bends, valves, constrictions, and even the internal roughness of the pipes. And let’s not forget leaks, which still account for nearly 20% of the volume produced in France (source: French Ministry for Ecological Transition, 2023). Not only do they squander a valuable resource, but they also cause the overall network pressure to drop.

A few things to keep in mind when talking about pressure

In the world of water networks, several specific terms are used to describe pressure:

MAP (maximum allowable pressure): this is the maximum pressure (even momentary, such as during a water hammer, i.e. a sudden overpressure phenomenon) that a pipe can withstand without risk.

AOP (allowable operating pressure): this is the maximum pressure that the pipe can withstand in continuous, daily service.

ATP (allowable test pressure): this is the pressure tested on a new pipe before it is put into service to verify that it complies with standards.

MDP (maximum design pressure): this is the maximum pressure anticipated by the network designer, taken into account from the design stage onwards.

OP (operating pressure): the pressure measured at a specific moment in time, at a given point in the network.

SP (service pressure): the pressure available at the connection point on the user’s premises, at zero flow rate.

Water hammer: an invisible but powerful wave

Finally, it is difficult to talk about pressure without mentioning water hammer. This phenomenon corresponds to a sudden change in pressure, often caused by a valve closing too quickly or a sudden change in flow rate. It can generate serious “shock waves” in the pipes, which can even cause them to burst if the equipment is not built to withstand them. Therefore, it is important to be fully aware of the maximum allowable pressures and to design the network by taking these constraints into consideration.

It is also important to note that flow rate and pressure are linked: if water flows faster through a pipe, the pressure decreases. This is described by Bernoulli’s equation, a relatively simple principle of physics: at constant energy, when velocity increases, pressure decreases.

In France, regulations (Article R1321-58 of the Public Health Code) require that wherever drinking water is available (up to the main meter), there must be at least three metres of pressure head, which is equivalent to a minimum pressure of approximately 0.3 bar.

But rest assured: in practice, the pressure at the tap is nearly always much higher. On average, there is:

2 to 3 bar of pressure at the tap, which is sufficient for normal domestic use (shower, washing machine, etc.).

3.4 bar on average at the meter, with values recorded on French networks between 3 and 5.2 bar depending on the area.

In some cases, especially for buildings with more than six storeys, the natural pressure of the network is not sufficient to reach the upper storeys. Boost pumps are then installed. These are devices that increase the pressure to ensure that everyone has water, even those at the top.

Last but not least, keep in mind that local water services may set additional requirements depending on the needs or specific characteristics of the network.

For continuous monitoring in the field, specially designed data loggers are used. The Claire Connect BLUE-LP logger is an excellent example. It is equipped with an internal pressure sensor (range 0-25 bar, certified for drinking water). Quick and easy pressure measurement can also be carried out directly on the network, for example by connecting via a quick coupling to a fire hydrant or pipe. The BLUE-LP logger also has an input for an external pressure sensor if required.

In addition to operational monitoring, preliminary pressure tests are carried out when new pipelines are put into production. These “pressure test trials” aim to check the network’s seal and structural strength under high pressure. A standard protocol (such as protocol 71 of the CCTP - Special technical specifications) is often followed. The test involves using a test pump to pressurise the section for a specified period of time (e.g. 5 minutes, then maintain for 30 minutes) and measuring the pressure variation with a suitable device.

The BLUE-LP logger, designed for network diagnostics and monitoring, records up to 500,000 values. It can transmit this pressure data independently (along with flow rates and meter readings) either to a customer supervisor or to the Ijitrack web platform, which can then issue alerts in the event of an anomaly.

What is the benefit of good pressure and flow management in the water network?

Measuring pressure and flow in a water network is not just for the sake of numbers: it is a powerful tool that makes it possible to manage, improve and maintain infrastructures more effectively. So, on a practical level, why is this so important?

Improved network performance and efficiency: by monitoring flow and pressure, the correct settings can be adjusted to ensure that the entire network operates efficiently. This helps to prevent waste, ensure that water is distributed more evenly, and guarantee a high-quality service.

Minimised water loss: by monitoring these indicators, it is easier to identify problem areas: a drop in pressure or abnormal flow may indicate a leak. Tools such as the BLUE logger, which can monitor an entire area from a single point, are very useful for quickly detecting and pinpointing these anomalies.

Preserved water resources: fewer losses directly equates to less waste. And considering that drinking water is a precious and limited resource, managing it better today means guaranteeing that future generations will have access to it.

Regulatory compliance: the law requires that minimum pressure be maintained throughout the entire network to guarantee access to water. Through continuous monitoring, we ensure that everything remains compliant with legal requirements.

Proactive maintenance and fast response: having real-time data means that teams in the field can react quickly as soon as a change is detected. This prevents minor problems from escalating into major disruptions.

Improved knowledge and management of the network: the data collected (pressure, flow rate, volumes consumed) is fed into digital tools such as the Ijitrack platform. These systems give us a better understanding of how the network behaves and let us adjust our actions, such as remotely controlling when a valve opens with Wayve boxes.

Sustainability of infrastructures: A carefully monitored network, where pressures are controlled and anomalies are quickly dealt with, wears out less quickly. This prevents premature deterioration and ensures that installations remain reliable and last longer.

Flow and pressure are the lifeblood of drinking water networks. Measuring, understanding and managing them effectively are fundamental actions to guarantee network performance, combat losses, preserve resources and deliver a high-quality service to users, both today and in the future.

The Claire Group is wholly committed to this approach, providing rugged equipment and innovative monitoring solutions. Tools such as the BLUE logger embody this capacity for innovation, providing industry professionals with the technical means to carry out accurate diagnostics, continuous monitoring and effective management of their networks. By providing the right information at the right time, these solutions enable network asset management to be optimised, thereby contributing to the safety and security of the water supply for future generations.

Controlling flow and pressure in water networks: the keys to sustainable performance

What is flow rate in a water network?

How can the flow rate of a water network be measured?

Essential precautions to follow when installing a flow meter:

What is pressure in a water network?

How is pressure measured in a water network?

What is the benefit of good pressure and flow management in the water network?