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Water Treatment for Closed Heating and Cooling Systems (BG 50/2013)

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BG 50/2013 guide replaces Water Treatment for Building Services (AG2/93) in respect of closed building services. Provides an introduction to theory of practice of water treatment in closed systems for design engineers, installing contractors and maintenance staff.

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Please note, BG 50 is in the process of being updated. A new edition will be published later in 2021. The update is being carried out by a technical author and steering group, in conjunction with the Closed Systems Control Association (CSCA), the British Association of Chemical Specialities (BACS), the Water Management Society (WMSoc), the Commissioning Specialists Association (CSA), the Institute of Workplace and Facilities Management (IWFM), the Institute of Corrosion (ICorr) and the Industrial and Commercial Energy Association (ICOM). A draft of the guide is currently available for wider industry consultation.

If you would like to comment on this draft, please email BSRIA’s publications manager, David Bleicher:


Water Treatment for Closed Heating and Cooling Systems (BG 50/2013) guide partially replaces Water Treatment for Building Services Systems (AG 2/93) with respect to closed system applications.

This guide provides an introduction to current theory and practice of water treatment in closed building systems. It is intended for use by design engineers, installing contractors and the maintenance staff responsible for looking after the completed systems. In particular it will help facilities managers and others choose the most appropriate water treatment for their systems.

The treatment of water in modern closed heating and cooling systems is essential for the avoidance of microbiological fouling (biofouling), corrosion and scale. These problems can result in energy wastage, poor system performance and the need for early replacement of plant and components. Many facilities managers have minimal understanding of how water treatment works, what it is intended to achieve and the consequences of ineffective water treatment can sometimes be disastrous.

The objectives of a water treatment programme are to maintain the system efficiency and cleanliness and prolong system life. The guide explains how to achieve this through:

  • system design
  • installation, testing and pre-commission cleaning
  • application of a correct and appropriate water treatment programme
  • effective management of the programme

The technical content of the publication has been compiled by a steering group comprising of BSRIA, the British Association for Chemical Specialities, the Water Management Society, the Commissioning Specialists Association and the United Kingdom Water Treatment Association.

The guidance is consistent with (BG 29/2012) Pre-Commission Cleaning of Pipework Systems, BS 8552:2012 Sampling and monitoring of water from building services closed systems. Code of practice and the European Biocidal products Regulation (528/2012, commonly known as BPR).

Product details

  • Published: October 2013
  • Publisher: BSRIA
  • Author: Edited by Reginald Brown
  • ISBN-13: 9780860227243

Common customer questions & answers

QQuestion I am aware that Figure 1 Dosing pot, on page 11 of BG 50/2013, shows an additional ‘safety’ check valve between the funnel and the body of the dosing pot. I personally and professionally feel that by adding a valve as a ‘safety’ feature, such a valve must be ‘safe’. The real issue for me is that it creates a false sense of security, as the intent/statement of protecting from a face full of chemical is incorrect. Not having a valve is better than having one that does not work as expected – there is no false security and if the operator follows the manufacturer’s O&M then the risk is minimised appropriately.
AAnswer Figure 1 illustrates one possible configuration of a generic dosing pot and is not intended to represent a recommendation or specification. There are various possible configurations of dosing pot and differing opinions in the industry on the benefits of including a check valve or not. Where a diagram or illustration is provided to support a specific recommendation this should be evident in the text. In this case the choice is left to the system designer.
QQuestion The guidance in BG 50 in some cases differs from that in BG 29. In these cases, which takes precedence?
AAnswer The two guides differ in their applicability – BG 29 for systems up to practical completion or up to a maximum of three months from pre-commission cleaning, and BG 50 for systems at any point in the life of the system from three months after pre-commission cleaning. Where guidance is given which has the same applicability (for example guidelines for practical completion) but which differs between the two guides, the most recently-published should be followed. As part of the current process of updating BG 50, any guidance with the same applicability will be harmonised with that in BG 29.