This article covers:
- Why is accurate specification important in water systems?
- The role of specification in building compliance and safety
- What do we mean by under-and over-specification?
- Causes of under-and over-specification
- How under-and over-specification impacts projects
- How CPD training improves specification accuracy
- Build confidence in water system specification with CIBSE-Approved CPD
- Under- and Over-Specification: FAQs
Getting the specification right is one of the most consequential decisions in building services engineering. Inaccurate specification is a persistent problem in the procurement of water and pump systems, and the costs are significant, from timeline complications to buildings that simply do not perform as intended.
Designers must make proportionate decisions to avoid both over-specification and under-specification. Yet many engineers rely on rules of thumb or outdated standards, often resulting in under- or over-specification.
Dutypoint has been supporting engineers in the design and specification of fluid and pump systems for over 50 years, and we have condensed that expertise into our CIBSE-approved CPD training modules. In this article we discuss how this training can support accurate specification on your next project.
Article Overview
Selecting equipment that is either under- or over-specified can increase costs, reduce system efficiency and create long-term operational challenges. CIBSE-approved CPD equips engineers with the technical knowledge needed to assess application requirements accurately, helping ensure building services equipment is specified correctly for performance, compliance and whole-life value.
Why is accurate specification important in water systems?
Accurate specification determines how a water system performs in practice. Correctly specified equipment will meet the building’s demand requirements, supporting long-term functionality. Additionally, in water system design, the correct specification of equipment, such as backflow devices, is essential for regulatory compliance and protecting public health.
Benefits of accurate specification
- Mitigates the need for redesign or project delays.
- Delivers required flow, pressure, and system performance.
- Optimises capital expenditure and long-term operating costs.
- Protects water quality and public health.
- Meets the required regulatory and compliance standards.
The role of specification in building compliance and safety
Specifications translate operational and regulatory requirements into measurable, technical criteria. This gives a fixed expectation to the manufacturer or supplier for systems like fire safety and water boosters, ensuring that the end product adheres to strict health and safety standards.
For dutyholders, specification documentation also serves as an audit trail of competent decision-making and compliance throughout the project. In higher-risk developments, specifications should provide clear detail to withstand regulatory scrutiny and facilitate approval processes mandated by the Building Safety Act.
Key frameworks influencing specification include:
- Building Safety Act 2022: Outlines dutyholders’ competence and documentation requirements.
- BS EN 806 & BS 8558: Provides core methodologies for calculating flow rates and sizing.
- Water Supply (Water Fittings) Regulations: Defines requirements for backflow protection.
- HSE ACOP L8: Defines system design requirements for effective Legionella prevention.
What do we mean by under-and over-specification?
Under-and over-specification describe two ways a system, such as a water booster system, can be incorrectly designed against actual building requirements.
Under-specification
Under-specification occurs when the design either does not define enough detail regarding demand requirements or severely underestimates them. This results in a water system that cannot meet required performance or compliance criteria.
Examples of under-specification in water systems
| Parameter | Example of under-specification | Consequence of under-specification |
| Flow | Peak demand underestimated | Insufficient supply at peak demand |
| Pressure | Booster set undersized for building height | Low pressure at upper floors |
| Storage volume | Tank too small for occupancy levels | Risk of water supply cutting out |
| Pipework | Pipe diameter undersized for demand | Reduced flow and poor performance |
| Backflow | Incorrect fluid category protection specified | Risk of public water contamination |
Over-specification
Conversely, over-specification occurs when the design demands a higher level of performance, complexity, or capacity than the project requires. As a result, the water system exceeds actual operational needs, adding unnecessary cost and inefficiency.
Examples of over-specification in water systems
| Parameter | Example of over-specification | Consequence of over-specification |
| Flow | Peak demand overestimated | Oversized plant increases energy use consumption |
| Storage volume | Tank oversized beyond occupancy requirements | Increased stagnation and contamination risk |
| Pipework | Pipe diameter oversized beyond requirements | Low velocity and increased stagnation risk |
| Backflow | Overly complex device selected for purpose | Unnecessary cost and maintenance burden |
Causes of under-and over-specification
Under- and over-specification can result from one or multiple factors. In M&E projects, they often arise from errors in how information is calculated, interpreted, communicated or managed across the design and delivery process. Key causes include:
Inexperience & lack of confidence: Teams who lack expertise or confidence in modern calculation methods may default to conservative estimates, resulting in oversized systems.
Defensive engineering: Experienced practitioners who rely on outdated standards to mitigate liability risks may produce conservative over-specifications.
Poor communication & coordination: Unclear briefs and poor cross-disciplinary coordination lead to incorrect assumptions and inaccurate system sizing.
Commercial pressures: Prioritising speed and budget over technical analysis can lead to convenience-driven shortcuts and reduced accuracy.
Regulatory complexity: Difficulty navigating overlapping frameworks results in specifications that may adhere to obsolete standards, therefore failing to meet compliance requirements.
Limited system knowledge: Professionals who lack expertise in fluid technology may rely on default suggestions, resulting in water systems that fail under real-world conditions.
Resource constraints: Organisations struggle to find the time and budget for ongoing training, so the knowledge gap continues to widen, risking further specification issues.
These factors can reinforce each other; a team that is under-trained, poorly coordinated, and operating under pressure in a complex regulatory environment is at significant risk of producing specifications that are either too conservative or too optimistic.
How under-and over-specification impacts projects
Inaccurate specification reduces how effectively a project moves from design through to completion and operation, due to the misalignment between what was required and what is ultimately delivered. Even small inaccuracies at design stage can escalate into major issues during delivery and operation:
- Timeline delays caused by failed commissioning and system redesign.
- Legal failures under Water and Building Regulations create compliance risk.
- Cost overruns especially where the system must be redesigned and replaced.
- Energy inefficiency from over-sized systems, running up long-term operational costs.
- Increased maintenance issues due to incorrect operating conditions.
- Occupant impact from poor pressure, system noise, or water quality.
- Reputational risk for consultants and contractors due to poor management and specification.
Project risks translate into very practical, expensive failures when they move from the page to the live site; for example, take a look at these two under- and over-specification scenarios.
Scenario 1: Water booster under-specification for a hospital
In a hospital redevelopment, a booster set was under-specified using outdated occupancy data. During peak demand, upper floors lost water pressure entirely. This necessitated an expensive emergency system replacement and a three-week delay in ward handover, triggering penalty clauses and compromising patient care standards.
Scenario 2: Oversized water storage tank for school development
A school development specified oversized storage tanks to future-proof the site. This caused low water turnover and stagnation, leading to dangerous Legionella levels during the first term. The client faced high remediation costs, system chlorination, and significant reputational damage before the building was safe to use.
Inaccurate specifications can have significant impacts, but they can often be prevented with regular engineering-informed training in system specification.
How CPD training improves specification accuracy
Accurate specification requires current, system-specific knowledge applied to the actual parameters of the project in hand. CPD training reduces specification risk by providing consultants the technical foundation needed to move beyond guesswork, and towards evidence-based design.
What does ‘good’ specification look like?
A good specification:
- Explicitly states clear and measurable performance and criteria.
- Is built upon accurate calculations, proportionate to actual demand requirements
- Aligns with current compliance standards and regulations.
- Requires clear, coordinated communication across multi-disciplinary teams.
- Optimises design for performance, efficiency, and maintainability.
Achieving that standard requires M&E professionals to be comfortable with technical concepts relevant to the required system. In fluid and pump systems, concepts that support accurate specification include:
- System-specific technical knowledge
- Understanding of flow, pressure, and demand modelling
- Awareness of regulatory frameworks and compliance requirements
- Ability to interpret site conditions and constraints
- Integration with wider building systems and controls
Consultants and contractors are best equipped to produce, or sign-off, specifications when they have a solid understanding of the above concepts. Industry-led CPD training improves specification accuracy by strengthening understanding of these concepts and their real-world application, enabling informed, defensible decision making.
Build confidence in water system specification with CIBSE-Approved CPD
Dutypoint’s application-led, CIBSE-approved CPD training is designed specifically for M&E consultants, contractors and engineers looking to expand their knowledge and confidence in specifying fluid and pump systems accurately. With over 50 years of hands-on experience in designing and commissioning water and pump systems for complex buildings, we deliver training that connects real-world specification challenges to the technical knowledge engineers need to resolve them.
Specification-focused CPD training
Cold-water Boosters Sizing & Selection
Gain the confidence to specify right sized booster sets that guarantee peak-demand performance while significantly reducing energy waste and capital expenditure. This session covers the essential methodologies for calculating required pressure and flow as per the BS EN 806 and CIBSE Guide G.
Packaged Utility Rooms – Design & Specification
Streamline the design and installation process by ensuring packaged units are perfectly tailored to the specific hydraulic and spatial needs of your project. This session focuses on the intricacies of specifying integrated utility rooms, including pump sets, tanks, and controls.
Offsite Packaged Plant Rooms
Achieve better quality control and faster project delivery by specifying standardised, factory-tested systems that meet rigorous safety and performance standards. In this session, we’ll show you how to plan layouts early and how to prevent key design and spacing issues that cause costly delays and installation errors.
Benefits of Dutypoint’s CPD training
✔ 50 years of industry experience allows you to leverage decades of specialist knowledge
✔ Application-led focus ensures training stays grounded in real-world scenarios.
✔ CIBSE-accredited CPD training that counts towards annual CPD recommendations.
✔ Flexible delivery via Microsoft Teams, on-site, or at our offices suits any team.
✔ “Lunch and Learn” 20-30 minute sessions make fitting professional development easy.
✔ System-specific knowledge supports accurate and confident specification of complex fluid systems
Dutypoint’s CIBSE-approved CPD training is designed to address real-world specification challenges, helping engineers so you can reduce project risk, and specify compliant systems with confidence.
Ready to reduce specification risk on your next project?
Book a “Lunch and Learn” CIBSE-accredited CPD course today to strengthen your water system knowledge and start making confident, optimised specification decisions.
Under- and Over-Specification: FAQs
Over-specification is typically caused by excessive safety margins, risk-averse design behaviour, poor coordination, and outdated assumptions. These factors compound across project stages, resulting in oversized systems that increase capital cost, energy use, and operational inefficiency.
Rightsizing is the process of matching system capacity precisely to actual building demand. It avoids unnecessary oversizing while ensuring compliance and performance, supporting energy efficiency, water quality, and long-term system reliability in modern building services design.
Key standards include BS EN 806 for system design, BS 8558 for application guidance, and Water Supply Regulations for backflow protection. These frameworks ensure systems are sized, installed, and operated safely, efficiently, and in compliance with legal requirements.
Specification accuracy is primarily the responsibility of the principal consultant, supported by contractors and specialists during delivery. Clear coordination between all parties is essential to ensure systems meet performance, compliance, and operational requirements.
The Golden Thread, introduced under the Building Safety Act 2022, is a complete digital record of all safety-critical specifications and installations maintained throughout a building’s lifecycle. Specifications must be accurate, auditable, and retained from design through handover and operation.
CPD training reduces specification risk by improving technical knowledge, calculation accuracy, and understanding of real-world system behaviour. It replaces outdated rules of thumb with evidence-based methods, enabling engineers to make confident, proportionate design decisions.
CIBSE-approved status means the institution has rigorously vetted the training for technical accuracy and educational quality. This accreditation ensures the content provides high-value knowledge that aligns with current building services industry standards.
From January 2024, CIBSE members must complete two annual semi-structured activities on building safety and sustainability. With no minimum hour requirement, the priority is enhancing professional competence through high-quality, relevant learning outcomes.
