The Selection of Expert Witness Advice on Water Industry Matters

G E Findlay B Sc, LLB., C Eng., C.WEM., M I C E., M I Mech E., MCIWEM., MIWSA
Director, Sewage and RBC Solutions Ltd.

1.0 Synopsis

1.1 This article is intended to offer guidance to parties seeking to instruct an Expert Witness in water related disputes specifically in relation to sewerage matters.

1.2 It suggests that when making such a selection it is imperative that the Expert Witness should have had design and construction experience gained as a staff member of one of the 10 UK water companies privatised in 1989.

2.0 Introduction.

2.1 When faced with possible legal action the Solicitor or his client may feel the need to appoint an Expert Witness. Selection may not always be straight forward.

2.2 The wrong selection could lead to increased costs or ultimate failure, even when the Expert seems to be very capable but lacks experience gained whilst working as an internal privatised water company employee.

3.0 Technical Standards

3.1 The UK Water Industry has its own technical standards developed over 40 years and continually updated all of which might not be published and therefore at variance with standards commonly in use by external organisations.

3.2 Certain bodies employ different parameters specific to their circumstances. No where is this more relevant than where per capita design figures are employed.

3.3 The Water Industry “in – house” standards will be in the form of a Design Manual which may not be universally shared outside of the company. Indeed, standards vary from company to company or even across a region but are based on very careful investigation and research and needed to minimise construction costs. Consequently, a very capable, highly experience Expert lacking “in – house” experience may inadvertently use the figures with which he is familiar albeit seriously at variance with the water company’s latest design standard.

3.4 One water company may employ a domestic per capita consumption of about 130-135 litres per day whereas an adjacent company may use 143-150. The difference may not be great, but it may be significant if the Expert analyzing a supposedly defective sewer choses to base his analysis on higher, widely publicised data.

3.5 A family of four adults may consume a total of between 520 -600 litres per day.

3.6 “Sewers for Adoption-A Design and Construction Guide for Developers” (“SfA”) is published by WRc plc. And reviewed by senior professional water company staff provides extremely valuable and worthwhile advice to developers and certainly should not be ignored.

3.7 The 6th Edition suggests that: -

”the design of gravity sewers for residential development should be 4000 litres / unit dwelling / per 24 hours“ (Page 27 paragraph 2.12)

3.8 This equates to 1000 litres per day where the occupancy rate is four. Since the average occupancy rate is more likely to be about 2.4 to 2.8, the per capita allowance is higher still.

3.9 Similarly, suppliers of mechanical equipment may also use a different figure. Consequently, it is important to appreciate which applies.

3.10 There are however perfectly valid reasons for using these guidelines and it is certainly not the intention of this article to in any way suggest otherwise.

3.11 Quite rightly any sewer designed using the “SfA” figures will almost certainly be much larger than that using the lower the “in-house” figure. Consequently, it is a matter of judgement which figure to use and a matter of understanding of water industry practise and intention to interpret.

3.12 It may be unwise for an Expert to claim that the sewer designed by the water company’s “in-house” design staff is too small if it fails the “SfA” criteria. Equally so it may be wrong to claim the converse when analysing a developer’s proposal where “SfA” properly applies. It may even be foreseeable that the Expert is unaware of the existence of the lower figures if he has never been involved or is new to “in-house” design.

3.13 Both figures are correct in their appropriate circumstances. Indeed, it can be argued that it is a complicated matter of judgment which criteria should be used where networks are being analysed but it should be appreciated by the experienced water professional particularly if he has “in-house” experience or knowledge.

3.14 The Expert must use the figure appropriate to the circumstances and fully understand the design philosophy before advising his client. More so, the Solicitor should look carefully to ensure the expert has the correct experience before instructing him.


3.15 Where flooding is the reason for litigation, the Expert’s analysis of the sewerage system based on “SfA” figures, may suggests the cause is due to the water company’s design being too small. The Expert may, however, find it embarrassing, if it is later shown in court that the sewer was designed in accordance with company policy, and that the sewer is adequate, and flooding is caused by some other undisclosed reason.

3.16 The water company would be able to explain why they were not obliged to use “SfA” and to show not only that their calculations are correct but have been successfully used across the U K water industry.

3.17 There will however be circumstances where “SfA” is the correct figure to use and it is not the intention of this article to suggest otherwise.

3.18 In order minimise costs the U K Water Industry have been very active in improving their standards in several areas not exclusively pipeline design consequently it is important that those standards are fully understood by the Expert Witness.

4.0 Conclusion

4.1 Water Companies policy may differ from those of other bodies and may not be published. Therefore, Solicitors seeking to instruct Experts in water related matters need to ensure the Expert has had the necessary level of experience within a U K Water Company. The Expert Witness should fully understand the water company policies and internally proven standards. Ignorance may adversely affect the outcome of the litigation.



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