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For many years, water treatment was treated as a downstream decision, typically left to the installing engineer. However, since June 2022, Approved Document L has directly referenced BS 7593:2019, effectively transforming guidance into a recognised way to demonstrate compliance with Building Regulations.
For M&E consultants, architects, contractors and building services engineers, this represents a fundamental shift. Water treatment is now best addressed at design stage, not deferred to site.
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As Nisar Afsar, Technical Director at Sentinel, noted, the direct reference within Part L means that the provisions of BS 7593 now carry considerable practical weight. Where water treatment is not properly specified, demonstrating compliance becomes considerably more difficult.
At the same time, many specifiers will recognise a familiar issue. Even where a brand is named in the specification, it may be substituted during installation. The challenge, therefore, is not only to specify correctly, but to do so in a way that protects the specification from being changed on site.
BS 7593:2019+A1:2024 is a code of practice covering the preparation, commissioning and ongoing maintenance of closed-loop heating and cooling systems. While originally focused on domestic systems, its principles are now widely applied across commercial and multi-residential developments.
It applies to traditional boiler systems and also to heat pumps, HIUs and communal heating systems in blocks of flats. Because it is referenced within Approved Document L, it now serves as the accepted benchmark for demonstrating that a system has been designed, installed and maintained in line with regulatory expectations.
The most significant change for specifiers is that leaving water treatment to the contractor to confirm risks ambiguity.
Instead, the specification should clearly define both the products and the processes required to meet BS 7593. This includes referencing the standard explicitly within NBS clauses and ensuring that water treatment is fully coordinated alongside the wider building services design.
Product specification plays a key role in protecting compliance. For example, naming an inhibitor such as Sentinel X100 Inhibitor, or an equivalent NSF-approved product, helps ensure that performance criteria are met and reduces the likelihood of unverified alternatives being introduced on site.
Similarly, BS 7593 also recommends the installation of a permanent in-line filter, and the specification should make clear that the filter should be capable of capturing both magnetic and non-magnetic debris. This ensures that minimum-compliance or inappropriate products are not installed.
Although BS 7593 is detailed, its core recommendations are actually quite straightforward.
Specifying in line with BS 7593 is not simply about regulatory compliance. It has a direct and measurable impact on system performance, energy efficiency and appliance lifespan.
Poor water quality leads to fouling, corrosion and reduced heat transfer efficiency. By contrast, correctly treated systems can deliver significant energy savings, with studies indicating reductions of up to 17% in boiler systems and as much as 27% in heat pump systems. Over the lifecycle of a building, this represents a substantial operational benefit.
There are also important commercial and legal considerations. Many boiler and heat pump manufacturers now require compliance with BS 7593 as a condition of their warranties. If a system is not correctly specified and maintained, those warranties may be invalidated, exposing building owners and project teams to avoidable risk.
Documentation also plays a role. The Benchmark commissioning checklist provides a formal record that the system has been installed and commissioned in accordance with recognised standards, offering protection in the event of disputes or performance issues.
The rise of heat pump systems has further increased the importance of getting water treatment right at design stage. These systems operate at lower temperatures, which increases the risk of microbiological activity and makes them more sensitive to fouling.
As a result, the recommendations of BS 7593 are particularly relevant. Biocide treatment is strongly recommended, and the interaction between glycol and inhibitor chemistry should be properly considered. Filter selection is also more critical, as heat pumps can be adversely affected by even small amounts of debris.
The potential benefits are equally significant. Because heat pumps rely on efficient heat exchange, maintaining clean system water has a greater proportional impact on performance than in traditional boiler systems.
A compliant heating specification should clearly reference BS 7593:2019+A1:2024 and define how its recommendations will be met. This includes naming an appropriate inhibitor product, specifying the requirement for a permanent in-line filter and setting out expectations for system cleaning, commissioning and maintenance.
It should also provide for ongoing verification, including annual water testing and long-term inhibitor management, and require completion of the Benchmark commissioning checklist as part of the project handover.
By addressing these elements at design stage, specifiers can ensure that compliance is built into the system from the outset, rather than relying on site decisions that may compromise performance or regulatory alignment.
In conclusion, water treatment is no longer a secondary consideration; it is an integral part of heating system design. A vague or incomplete specification creates risk, while a clear and detailed one protects performance, compliance, and long-term value.
By embedding BS 7593 guidance into the specification, consultants and engineers can ensure that their designs are not only compliant, but robust, efficient, and protected throughout the lifecycle of the building.
For a structured approach to achieving this, including product selection and system best practice, you can find the Sentinel guide here:
