DOC

Chapter 2 - Ofwat Ofwat home page

By Zachary Price,2014-08-17 11:56
9 views 0
Chapter 2 - Ofwat Ofwat home page

    Page 1 of 20

    Section 2 Chapter 2

    Chapter 2

    Key outputs

    Water service - 2

    Covering:

    DG2 Pressure of mains water

    DG3 Supply interruptions

    DG4 Restrictions on use of water

    June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 2 of 20

    Section 2 Chapter 2

    Chapter 2

    Key outputs

    Water service 2

DG2 Properties receiving pressure/flow below the reference level

    The aim of this indicator is to identify the number of properties that have received and

    are likely to continue to receive pressure below the reference level when demand is not

    abnormal.

DG3 Properties affected by supply interruptions

    The aim of this indicator is to identify the number of properties affected by planned and

    unplanned supply interruptions lasting longer than 3 hours, 6 hours, 12 hours and 24

    hours.

Population.

DG4 Restrictions on use of water.

    The aim of this indicator is to identify the population affected by restrictions on water

    use and their duration.

    The information in this table is used to monitor and compare company performance against the DG indicators. It is published, in summary, in the annual ‘Levels of Service’ report.

    Lines 1 to 4: DG2 Properties receiving pressure/flow below the reference level

Aim

    To identify the number of properties which have received and are likely to continue to receive pressure below the reference level when demand is not abnormal.

Common definitions

    To ensure consistency of information returns the following regularly used terms are defined below:

    Reference level: The reference level of service is a flow of 9l/min at a pressure of 10m head on the customer's side of the main stop tap (mst). The reference level applies to a single property.

    The reference level of service must be applied on the customer's side of a meter or any other company fittings that are on the customer's side of the main stop tap.

    Where a common service pipe serves more than one property, the flow assumed in the reference level must be appropriately increased to take account of the total number of properties served.

    For two properties, a flow of 18l/min at a pressure of 10m head on the customers' side of the mst is appropriate. For three or more properties the appropriate flow should be calculated from the standard loadings provided in BS6700 or Institute of Plumbing handbook. See below for a tabulation of minimum mains pressures for the reporting of low pressures on common services.

June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 3 of 20

    Section 2 Chapter 2

    Surrogate for the reference level: Because of the difficulty in measuring pressure and flow

    at the mst, companies may measure against a surrogate reference level. Companies should use a surrogate of 15m head in the adjacent distribution main unless a different level can be shown to be suitable. In some circumstances companies may need to use a surrogate pressure greater than 15m to ensure that the reference level is supplied at the customer's

    side of the mst (for example in areas with small diameter or shared communication pipes).

    Common supplies: Common supplies are where a communication pipe supplies more than one property. The required pressure in the adjacent water main used to estimate properties affected should exceed those given in the table in the guidance section. This table is intended to be a guide to the absolute minimum service acceptable over an hour (i.e. it is not based on an instantaneous peak flow). The calculations assume delivery of 9 l/minute upstairs to a combination tank (not in the loft) in the end property on a common service of half-inch bore. The calculations use the BS 6700 loading units (LU) basis, but at 3LUs per property (9 l/minute). The LU calculations on larger groups of properties (i.e. more than 100) give instantaneous flows of between 4 and 8 times the peak hour flow rates actually observed on local distribution systems, subject to leakage and hose pipe assumptions. Accordingly, the use of 3LUs per property is taken as an acceptable minimum.

Allowable exclusions: There are a number of circumstances under which properties

    identified as receiving low pressure should be excluded from the reported DG2 figure. The aim of these exclusions is to exclude properties which receive a low pressure as a result of a one-off event and which, under normal circumstances (including normal peaks in demand), will not receive pressure or flow below the reference level. The exclusions are:

     Abnormal demand: this exclusion is intended to cover abnormal peaks in demand and

    not the daily, weekly or monthly peaks in demand which are normally expected.

Planned maintenance.

One-off incidents: This exclusion covers a number of causes of low pressure:

    - mains bursts;

    - failures of company equipment (such as PRVs or booster pumps);

    - firefighting; and

    - action by a third party.

Low pressure incidents of short duration: Properties affected by low pressures

    which only occur for a short period, and for which there is evidence that incidents of a

    longer duration would not occur during the course of the year.

Incidents of short duration: In locations where companies carry out continuous

    pressure logging year round, low pressure incidents of less than one hour may be

    excluded from DG2.

    Where short term or intermittent logging is used, if all low pressure incidents lasting less than one hour are excluded there is a danger that properties which are actually below the reference level will be missed from the DG2 figures.

    In this case a suitable minimum duration depends on the exact methodology used but may be 30 or even 15 minutes. If logging is carried out at times when low pressures are unlikely to be detected because demand is low, the results cannot be used to confirm zero returns for DG2.

Guidance

Surrogate for the reference level: Where companies choose to report against a surrogate

    pressure of less than 15m, evidence must be provided that this is sufficient to provide the June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 4 of 20

    Section 2 Chapter 2

    reference level of service for all properties taking into account the length and condition of communication pipes and head loss through any meters or other company fittings. Any assumption made must be clearly stated in the methodology. A surrogate pressure which will only provide the reference level for average properties (i.e. for average length communication pipes in good condition with no meter fitted) is not appropriate because some properties will have communication pipes longer than average; others will be in a poor condition or have meters fitted. Allowance must be made in such instances.

    If a higher surrogate is used, the assumptions should be clearly stated in the methodology.

    Headline DG2 figure: This is an estimate of the total number of properties in the company's area that are below the reference level. Therefore, if the reported figure is likely to represent an underestimate (or an overestimate) this must be reflected in the assessment of the reliability and accuracy of the reported information.

    In practice companies will report the number of properties served by a main in which the measured pressure falls below the surrogate for the reference level (usually 15m head in the adjacent distribution main) subject to the allowable exclusions. The reported DG2 figure is not necessarily the same as the number of properties on the DG2 register, which should contain additional information and provide a wider database than a list of known DG2 problems.

    The figure for the start of the report year will be the figure from the end of the previous report year and will be downloaded from the previous June return.

    Estimated figures: Companies may include in their reported DG2 figures estimates for the number of properties which are below the reference level but which have not yet been specifically identified. It must be clearly stated in the commentary whether or not they include such an estimate for DG2 and, if so, the number of properties involved. The basis for the estimate must be explained in the methodology.

Section 65 of the 1991 Water Industry Act: In some circumstances companies do not have

    a duty to provide customers with a constant supply of water under pressure (usually because the properties cannot be supplied by gravity from an existing service reservoir). Nevertheless, such properties must be included in the reported DG2 figures if they receive a level of service below the reference level. Companies may record the number of these included in their reported figures in their commentaries

    Allowable exclusions: Companies must maintain verifiable, auditable records of all the exclusions that they apply in order to confirm the accuracy and validity of their information.

    All properties identified as having received pressure or flow below the reference level must be reported under DG2, unless it can be confirmed that they are covered by one of these exclusions.

Abnormal demand: See separate section.

Planned maintenance: Companies should not report under DG2 low pressures

    caused by planned maintenance.

    It is not intended that companies identify the number of properties affected in each

    instance. However, companies must maintain sufficiently accurate records to verify that

    low pressure incidents that are excluded from DG2 because of planned maintenance

    are actually caused by maintenance.

     One-off incidents: If problems of this type affect a property frequently, they cannot be

    classed as one-off events and further investigation will be required before they can be

    excluded.

Low pressure incidents of short duration: Properties affected by low pressures

    which only occur for a short period, and for which there is evidence that incidents of a June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 5 of 20

    Section 2 Chapter 2

    longer duration would not occur during the course of the year, may be excluded from

    the reported DG2 figures.

    Common services: Companies should establish the numbers of properties supplied via common services from sample investigation of the distribution system. Many instances of low pressure in these situations are presently unreported. Not all of these properties have either loft tank storage or any water supply upstairs.

    Companies are required to report the numbers of properties on common services that have received and continue to receive pressures below the reference level, and include these in the reported numbers under DG2. The commentary must state the number of properties on common services that have been included in the reported figures.

    Companies may use their own calculations but the required pressure in the adjacent water main used to estimate properties affected should exceed those given in the table below. This table is intended to be a guide to the absolute minimum service acceptable over an hour (i.e. it is not based on an instantaneous peak flow). The calculations assume delivery of 9 l/minute upstairs to a combination tank (not in the loft) in the end property on a common service of half-inch bore. The calculations use the BS 6700 loading units (LU) basis, but at 3LUs per property (9 l/minute). The LU calculations on larger groups of properties (i.e. more than 100) give instantaneous flows of between 4 and 8 times the peak hour flow rates actually observed on local distribution systems, subject to leakage and hose pipe assumptions. Accordingly, the use of 3LUs per property is taken as an acceptable minimum.

    Number of Pressure (in head) required in adjacent main

    properties fed

    from one Half-inch communication pipe Three quarter-inch communication

    direction on pipe

    common service

    Short side Long side Short side Long side

    2* 10 11 10 11

    3 12 14 11 13

    4 15 18 13 16

    5 19 23 16 20

    6 25 29 21 24

    7 30 35 25 28

    8 37 42 31 33

    9 45 51 38 40

    10 54 61 46 48

    Note: if delivery to a loft tank is taken to be the minimum acceptable service, not less than 3 m pressure should be added to the above tabulated values.

    * The values calculated for two properties are theoretical: for delivery to a loft, the usual surrogate of 15 m head to a single property should be taken as a minimum reference level.

    The section on the reference level refers to the need for companies to use a higher flow rate in the reference level for common services and sets out the criteria for determining appropriate flows in these circumstances.

    These criteria are not intended to extend the company's responsibility to solving problems caused by deficiencies in customers' pipes. Its aim is to ensure that there is a proper recognition of pressure and flow problems which affect properties sharing common services, where there is a deficiency in the part of the apparatus which is the company's responsibility (e.g. an undersized communication pipe which is unable to provide sufficient flow).

    For the purpose of DG2, properties with the common service pipes can be split into four categories:

    June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 6 of 20

    Section 2 Chapter 2

Company’s and customers' apparatus are adequate:

    - no problems with pressure or flow, nothing to report for DG2;

Company apparatus adequate, but customers' pipework is deficient:

    - pressure and/or flow problems which are not reportable under DG2 because company

    pipes are able to provide sufficient pressure and flow to the limit of company

    responsibility;

Company apparatus is inadequate but customers' pipework is adequate:

    - pressure and/or flow problems which are reportable under DG2 because there is a

    deficiency in the company's apparatus;

Both the company's and the customers' apparatus is inadequate:

    - pressure and/or flow problems are reportable under DG2.

Of these four categories, only the last two fall within DG2.

    Ofwat recognises that in cases covered by the final category it may not always be sensible for the company to take unilateral action to solve the DG2 problem unless the customer takes some action to improve their own pipework. Nevertheless, these problems must be included in the reported DG2 figure. If significant, companies should report in their commentary the number of properties which are below the DG2 reference level but the company cannot solve because there are also defects in the customer's part of the system.

    The commentary should also state the number of properties reported due to the effect of common service pipes. Company methodologies should discuss how common service problems are identified and assessed and include reference to standard loadings.

    In addition, companies are required to estimate the number of properties on common services that may receive pressures below the reference level. This information will provide a broad indication of the scale of the potential problems yet to be investigated; it is anticipated that, upon investigation, some but not all of these estimated properties may be included on the DG2 register in future years. These estimates must not be included in the reported figures, but highlighted in the commentary.

Abnormal demand: Some companies are more affected by low pressures caused by

    occasional prolonged peaks in demand than by a few abnormal peak days each year. In such cases, instead of excluding up to five days each year, companies may choose to apply the abnormal demand exclusion over a five-year period. This will allow companies to exclude from their DG2 figures properties affected by low pressures that occur on any 25 days in a rolling five-year period.

    For the purpose of DG2, the 'excluded day' may be applied to the company as a whole or at the level of individual zones. However, in either case, once a property has suffered low pressures on either more than five days in one year or 25 days in five years, it must be added to the reported figures for DG2.

    Companies must clearly state in their methodologies which approach they have adopted in applying this exclusion, list the distribution or supply zones they have chosen and the number of days excluded. If the exclusion is applied at the level of individual zones, rather than to the company as a whole, the company must maintain verifiable records which list the number of 'excluded days' used for each distribution zone each year.

    Option 1 - During the report year, companies may exclude for each property a maximum of 25 days of low pressure caused by abnormal demand in a rolling five-year period. Companies June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 7 of 20

    Section 2 Chapter 2

    should exclude from the reported DG2 figures properties that are affected by low pressure only on the days identified as "high demand" in the report year. In years where demand is normal (i.e. the exclusion is not being used), these companies will have to add to their DG2 figures all properties affected by relevant low pressure incidents (unless covered by one of the other exclusions).

    Option 2 - Where extensive pressure logging covering the majority of properties in the supply area is used, the company may exclude properties where logger records verify that up to five incidents of low pressure lasting more than one hour have occurred. Under this option, it is not necessary to match the low pressure incidents with high demands. Companies that choose this method must include the number of properties that suffer more than five incidents of low pressure lasting more than one hour in the reported figure without necessarily identifying the specific occasions and reasons for abnormal demand. If this method is used, no other allowance may be made for abnormal demand but the other exclusions still apply.

Records

    Companies must maintain verifiable records for DG2. The aim of the records is to provide an auditable method for identifying the specific properties affected by low pressures and the cause of the low pressure.

    The DG2 Register: Companies must maintain a register that should form a database of all properties that experience problems with pressure or flow.

    It will enable the identification by address of individual properties which are below the reference level. It should also contain information on, for example, complaints and the results of their investigation, problems which are attributable to customers' apparatus and properties which experience low pressure but are covered by one of the allowable exclusions.

    The register must clearly identify those properties reported under DG2 and distinguish them from those that receive low pressure but are excluded from DG2, and provide a verifiable reason for the exclusion (e.g. as abnormal demand or short duration of low pressure).

The records should include:

the address of the property affected;

the method of assessment;

the cause of low pressure;

    ;

     details of incidents identified (date, time, duration, minimum pressure, and whether

    covered by an exclusion);

action taken to resolve the problem (if any); and

the name of person responsible for the information.

    Properties should only be removed from the DG2 figures and the register when there is a specific and auditable reason for doing so.

June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 8 of 20

    Section 2 Chapter 2

    Company commentary

The company should:

comment on significant year on year changes in reported figures;

     state the number properties on common services that have been included in the

    reported figures;

     report in its commentary the number of common service properties which are below the

    DG2 reference level but the company cannot solve because there are also defects in

    the customer’s part of the system;

     state any assumptions and estimates made in reporting the figures; and

     state whether any allowance has been made for problems as yet undiscovered.

Guidance to Reporters

Reporters are asked to comment on:

whether methods used are appropriate to meet Ofwat’s reporting requirements;

     whether all assumptions have been disclosed and to comment on their materiality; and

the appropriateness of the confidence grades assigned;

Lines 5 to 19: DG3 Properties affected by supply interruptions

Aim

    To identify the number of properties affected by planned and unplanned supply interruptions lasting longer than 3 hours, 6 hours, 12 hours and 24 hours.

Common definitions

    To ensure consistency of information returns the following regularly used terms are defined below:

    Duration is defined as the length of time for which customers are without a continuous supply of water. An interruption starts when water is unavailable from the first cold tap in a property and finishes when the supply is restored.

    A third party is defined as anyone who does not act for, or on behalf of, the company. It therefore excludes agents, contractors and other parties acting with the authorisation of the company. This category is intended to cover damage to a company's mains or other equipment which either directly causes a loss of supply or which requires an unplanned interruption to supply to repair the damage inflicted.

Guidance

    Properties affected by interruptions: The number of properties affected by interruptions of more than 3, 6, 12 and 24 hours split into the four categories of unplanned; planned and warned; unplanned but caused by third parties; and unplanned due to overruns of planned and warned interruptions.

    Interruptions should be reported under each relevant time band so that the category for interruptions exceeding:

June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 9 of 20

    Section 2 Chapter 2

    3 hours also includes all interruptions lasting more than 6 hours;

6 hours also includes all interruptions lasting more than 12 hours; and

12 hours also includes all interruptions lasting more than 24 hours.

    Each interruption should be classed as a single interruption event, and should be recorded under only one of the four categories of: unplanned or unwarned; planned and warned; unplanned third party interruptions; or unplanned or unwarned due to overruns of planned and warned interruptions.

Properties affected by more than one interruption during the report year: Properties,

    which are affected by more than one interruption during the report year, should be reported separately for each interruption. This means, for example, that a property affected by three supply interruptions would be reported three times, once for each interruption. Where properties are affected by repeat interruptions on the same day, these should only be counted separately where there is sufficient time (eg 1 hour) between the interruptions for the supply to be available (eg to refill storage tanks).

    Duration: An interruption to supply is defined as starting as soon as water is no longer available from the first cold tap in the property. It does not necessarily commence when the company first takes action, for example, by closing a valve (the interruptions may have started some time earlier). Companies are expected to ascertain the approximate time when customers first lose their supply.

    In practice, it may not always be possible to determine when supply was first lost and companies may have to use the time when customers first noticed the loss of supply. If this cannot be established, companies should use the time at which they were first notified of the interruption.

    Third party: Properties affected by interruptions due to electricity supply failure must not be reported under this category. Instead they must be reported as unplanned, unwarned interruptions. However, companies may report in the commentary the number of properties affected by interruptions caused by loss of electrical supply, if it is believed to be significant and to adversely affect company performance.

    Planned and warned interruptions for 6, 12 and 24 hours respectively due to third parties should be classed as, and reported in lines 8 to 10.

    Major incidents: Companies may report in their commentary any major incidents during the report year that they believe adversely affected their DG3 performance.

    Information on the number of incidents that cause interruptions is not required.

    Planned interruptions: So far as customers are concerned there is no difference between unplanned interruptions and planned but unwarned interruptions.

Records

    Companies must maintain records of all incidents of supply interruptions lasting longer than three hours in the form of a DG3 register.

    The aim of the register is to allow verification and audit of the reported information for DG3 and to enable the identification of the properties affected. It should contain information on the timing, duration and cause of each interruption and sufficient information to enable all properties affected by interruptions lasting more than three hours to be identified. Therefore, the register should include:

properties affected (by name and location or number and street);

June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

    Page 10 of 20

    Section 2 Chapter 2

     date and time of interruption;

duration of interruption and time supply restored;

cause of interruption;

notice given; and

the name of person responsible for entering records in the system.

    The information in the DG3 register should be available for verification of incidents and claims for payment under the GSS.

Company commentary

The company should:

comment on significant year on year changes in reported figures;

     ensure comparability of information. Companies must report in the return tables against

    the DG's definitions, not companies' own internal standards. However, if companies wish

    to report additional information on performance against alternative standards this may be

    included in the commentary but the alternative basis must be clearly stated. Any figures

    relating to the alternative standard must be clearly identified as such to avoid confusion.

     identify in its commentary any properties which suffered an interruption to supply where

    the company considers that customers would not notice the loss of service, for example

    because it occurred at night;

     report the number of properties affected by interruptions caused by loss of electrical

    supply, if it is believed to be significant and to adversely affect company performance; and

     report any major incidents during the report year that it believes adversely affected its

    DG3 performance.

Guidance to Reporters

The Reporters should comment on:

whether methods used are appropriate to meet Ofwat’s reporting requirements;

     whether all assumptions have been disclosed and to comment on their materiality; and

the appropriateness of the confidence grades assigned.

    Reporters are asked to pay particular attention to company methodology for and the reporting of the duration of events, including intermittent events at the same location.

Line 20: Population

Company commentary

    The company should comment on significant year on year changes in reported figure.

Guidance to Reporters

The reporters should comment on:

June return reporting requirements and definitions manual 2006

    Issue 1.1 31 March 2006

Report this document

For any questions or suggestions please email
cust-service@docsford.com