Pressure or Flow? Unmasking the Culprit Behind Poor Water Performance
As a plumber, you've likely faced countless calls about "low water pressure." But as we know, the sensation of poor water performance isn't always a straightforward pressure problem. Often, the hidden issue is an inadequate flow rate to the property. Misdiagnosing the two can lead to incorrect solutions, wasted money, and a still-frustrated client. This guide will help you distinguish between a true pressure issue and a flow rate limitation, and outline the correct testing and solutions for each.
The Core of the Problem: Pressure vs. Flow Rate
Before diving into testing, let's clarify the difference:
Water Pressure: This is the force pushing water through the pipes. It's typically measured in kilopascals (kPa) or pounds per square inch (psi). Adequate static pressure (when no taps are open) is necessary, but doesn't tell the whole story. In Australia, mains water pressure typically ranges from 300 kPa to 500 kPa, though regulations often state it should not exceed 500 kPa at the property boundary.
Water Flow Rate: This is the volume of water delivered over a period, often measured in litres per minute (L/min) or gallons per minute (GPM). Flow rate is what actually allows multiple fixtures to run simultaneously without a significant drop in performance.
A property can have good static pressure but poor flow, or genuinely low pressure. The key is to understand how the system behaves under demand.
The Diagnostic Test: Unveiling the True Issue
A simple, effective way to determine whether you're dealing with a pressure or flow rate problem involves measuring pressure changes as demand increases:
Baseline Static Pressure:
Ensure all taps and water-using appliances on the property are turned off.
Connect a pressure gauge to a suitable point where the mains water enters the house, typically an outside tap or a connection near the water meter.
Record this initial pressure reading. This is your static pressure.
Single Tap Open:
Fully open one cold water tap (e.g., a bath or laundry tap).
Observe the pressure gauge and record the new reading (dynamic pressure). Note the drop from the static pressure.
Multiple Taps Open:
While the first tap is still fully open, fully open two additional cold water taps in different locations (e.g., another bathroom tap and the kitchen sink).
Again, observe the pressure gauge and record the pressure reading with three taps running. Note the total pressure drop from the initial static pressure.
Interpreting the Results
This is where the distinction becomes clear:
Significant Pressure Drop (Over 150-200 kPa): Indicates a Flow Rate Issue If the pressure drops dramatically (by more than 150-200 kPa) from the static reading when one tap is open, and significantly more as additional taps are opened, this strongly suggests an issue with the flow rate to the property. This means the mains supply pipe, or the connection to the mains, cannot deliver a sufficient volume of water to meet the demand, even if the initial static pressure seemed adequate. The restriction causes the pressure to plummet when water is drawn.
Consistently Low Pressure (Little Drop, But Low Overall): Indicates a Supply Pressure Issue If the static pressure is already low with no taps open, and it doesn't drop much further (e.g., less than 50-100 kPa) when one or even three taps are opened, this points to a genuine low supply pressure from the mains. In this scenario, the volume of water might be sufficient, but the force pushing it is inadequate.
Fixing a Flow Rate Issue: The Break Tank and Repump Solution
If your tests indicate a flow rate problem (significant pressure drop), simply installing a standard booster pump directly onto the incoming mains will not solve the issue, and can even make it worse.
Why a Booster Pump Won't Help a Flow Rate Problem: A booster pump is designed to increase the pressure of the water it receives. It cannot magically create more water volume than the mains pipe can deliver. If the incoming flow is restricted, the booster pump will attempt to draw more water than is available. This can lead to:
The pump running dry or cavitating, causing damage.
Further pressure drops in the mains, potentially affecting neighbouring properties.
No significant improvement in performance at the taps because the volume is still the bottleneck.
The Correct Solution: Break Tank and Repumping System To rectify a poor flow rate to the property, the most effective solution is to install a break tank (also known as a cistern or intermediate tank) and a repumping system.
How it Works:
The break tank is connected to the incoming mains supply. It fills slowly at the restricted flow rate the mains can provide, effectively acting as a reservoir.
An air gap within the break tank is crucial for preventing backflow and contamination of the mains supply, complying with plumbing regulations.
A separate pump (a booster pump) is then installed after the break tank. This pump draws water from the tank – which now holds a stored volume – and delivers it to the property's plumbing system at the desired pressure and flow rate.
Why it Works: The break tank "breaks" the direct reliance on the instantaneous flow rate from the mains for meeting peak demand. It allows water to accumulate, providing a buffer. The secondary pump then has a sufficient volume of water readily available in the tank to supply multiple outlets simultaneously without being starved by a restricted mains inflow. This system ensures both adequate pressure and adequate flow rate throughout the property.
Fixing a Supply Pressure Issue: The Standard Booster Pump
If your diagnostic test shows that the pressure is consistently low even with only one tap open, but it doesn't significantly drop further as more taps are opened, this indicates a true low supply pressure problem.
The Solution: In this scenario, a standard mains water booster pump can be an effective solution.
How it Works: The booster pump is installed directly on the incoming mains line (where regulations permit and no significant flow restriction exists). It takes the existing mains pressure and increases it to provide a better, more consistent pressure throughout the property.
Why it Works: Because the underlying issue is simply the force of the water, not the volume available, the booster pump can effectively elevate the pressure to an acceptable level for all outlets.
Important Considerations:
Internal Pipework: Always consider the condition and diameter of the property's internal pipework. Old, corroded, or undersized pipes can also cause poor flow and pressure drops, even if the mains supply is adequate. This should be assessed as part of your diagnosis.
Regulations: Ensure all installations comply with local plumbing codes and water authority regulations, particularly regarding backflow prevention when installing break tanks or connecting pumps to the mains.
Client Communication: Clearly explain your findings and the reasons for your recommended solution to the client. Helping them understand the difference between pressure and flow will build trust and justify the chosen approach.
By carefully testing and correctly diagnosing whether the problem lies with pressure or flow rate, you can implement the right solution first time, ensuring a happy client and a well-performing water system.
