Nature and the environment;Nature and the environment;Public sector
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Municipal wastewater


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Key figures

0.61 %

of the wastewater pipeline system was on average renewed in the last three years

Municipality-State-Reporting: wastewater
201220152016Change in per cent
2012 - 20162015 - 2016
Percentage of population connected to municipal wastewater facilities83.984.
Connection density of wastewater pipeline system (inhabitants/km)1181191190.80.0
Percentage of total wastewater pipeline system renewed, 3-year-average0.480.570.6127.17.0
Number of sewage overflow in sewage pipelines and manhole covers per km pipeline0.0540.0480.053-1.910.4
Income from fees per inhabitant connected to municipal wastewater facilities1 4291 6361 66116.21.5
Operating expenditures per inhabitant connected to municipal wastewater facilities9881 1301 16217.62.8

See more tables on this subject

Table 1 
Inhabitants connected to municipal and non-municipal wastewater treatment plants. Number of people.

Inhabitants connected to municipal and non-municipal wastewater treatment plants. Number of people.
All connected inhabitants5 029 0615 080 0005 123 825
Municipal4 303 7544 355 4854 392 616
Private725 307724 515731 209
Inhabitants connected to wastewater treatment plants 50 pe or more4 256 7594 313 6914 352 605
Municipal4 230 0194 286 4294 328 686
Private26 74027 26223 919
Inhabitants connected to wastewater treatment plants less than 50 pe772 302766 309771 220
Municipal73 73569 05663 930
Private698 567697 253707 290

About the statistics

Municipal wastewater is a statistics which describes topics in the water sector like municipal fees, self-cost, wastewater pipelines, treatment plants and people connected, compliance with treatment permits, sewage sludge etc. The statistics is part of the Municipality-to-State statistics (KOSTRA).


Definitions of the main concepts and variables

Wastewater facility without treatment is a discharge originating from wastewater facilities without treatment (commonly referred to as direct discharges). The discharge is connected to municipal pipelines, but it does not take place any form of treatment.

Operating expenditures constitutes the sum of direct operating expenditures and indirect operating expenditures. Data is derived from the KOSTRA-form number 23.

Cost coverage refers to, in percent, how big a share of the annual wastewater related costs the municipalities actually cover by wastewater fees. Municipalities are not entitled to claim more than actual costs, neither are they obliged to claim full cost coverage.

    Full cost ratio = ((Fee income) / (Fee calculation basis + Allocations - Use of funds)) x 100

Wastewater fees claimed by the municipality, consist of a connection fee and a wastewater fee. The connection fee is collected once only - during installation - while the wastewater fee is collected every year. The data for income from fees is derived from KOSTRA-form 23.

Capacity and load . The capacity of a treatment plant is the amount of wastewater it is designed to handle, while the load is the amount of wastewater a wastewater plant actually receives. The unit of both capacity and load is provided in population equivalents (pe).

High-grade wastewater treatment plants are those that provide a biological and/or chemical treatment phase. Biological treatment mainly removes readily degradable organic material using microorganisms. The chemical phase involves the addition of various chemicals to remove phosphorus. Certain treatment plants also have with special phases for nitrogen removal. High-grade plants reduce the amounts of phosphorus and other pollutants in the effluent more effectively than mechanical plants.

Investments are gross investments, omitted possible revenues on investment and sale of capital goods. County and state subsidies is included, the same applies to previous surplus from the wastewater sector. Data are derived from the investment account number 350 and 353. Investment is the sum of the following sub-accounts: 010:500, 690, 790. In order to make the calculations comparable with previous years (complete the time series), sub-account 700 and 810 (state contributions) and 730 and 830 (county contributions) is omitted here.

Capital cost consists of the following two costs: Depreciation of earlier annual investments and a calculated interest cost for capital goods. Both calculated interest cost and depreciation cost is derived from KOSTRA-form number 23.

Municipal wastewater facilities include all municipal wastewater facilities and treatment plants with a capacity of 50 pe or more. The facilities are generally divided into six groups: direct discharge, mechanical, chemical, biological, chemical-biological, and natural purification processes/other treatment.

Mechanical wastewater treatment plants include sludge separators, screens, strainers, sand traps and sedimentation plants. They remove only the largest particles from the wastewater, thus treatment efficiency in regards to nitrogen and phosphorus is relatively low.

The North Sea Agreements/OSPAR convention refers to the joint declarations made by the countries around the North Sea to reduce inputs of nutrients to this sea-area. One of the targets was to halve the total inputs of nitrogen and phosphorus during the period 1985 to 1995. Since Norway did not reach the nitrogen target by the end of 1995, the national time limit was extended to 2005. The North Sea Agreements applies to the areas south of the 62 o N. As for the nutrient reduction targets, only the counties with drainage into the Skagerak and North Sea, from the Swedish boarder to Lindesnes, are bound by the agreement.

North Sea counties entail the following counties: Østfold (01), Akershus (02), Oslo (03), Hedmark (04), Oppland (05), Buskerud (06), Vestfold (07), Telemark (08), Aust-Agder (09) and Vest-Agder (10). Practically all land areas in these counties drain into the Skagerak and North Sea.

Population equivalent (pe) is defined as the amount of oxygen consumed in 5 days when organic material is decomposed in water. When 1 pe is defined as 60 g BOD5, it means that 1 pe will bring in daily the amount of organic material that microorganisms need 60 g of oxygen to decompose within 5 days.

Wastewater treatment plants are generally divided into three main groups according to the type of treatment they provide: mechanical, biological or chemical. Some plants incorporate combinations of these basic types.

Individual wastewater treatment facilities are designed to handle wastewater equivalent to the amount, or composition, of no more than 50 pe.

Standard classifications

The 428 municipalities are grouped according to population and economic comparable groups. This is based on the report (in Norwegian only) Gruppering av kommuner etter folkemengde og økonomiske rammebetingelser Rapport 2011/8, Statistisk sentralbyrå

Administrative information

Name and topic

Name: Municipal wastewater
Topic: Nature and the environment

Responsible division

Division for Natural Resources and Environmental Statistics

Regional level

The figures are published on national and regional (municipal and county) level, in addition to grouped in economically comparable groups.

Frequency and timeliness

Key figures are published annually in connection with Municipal-State-Reporting (KOSTRA) on the 15th of Mars (unrevised) and 15th of June (revised).

International reporting

Not relevant


The raw data is saved in text-format. Revised data sets are saved in Oracle-databases here with Statistics Norway. The Norwegian Environment Agency also has a copy of the dataset.


Background and purpose

KOSTRA started up as a project in 1995 with the intention to provide relevant and up-to-date information about resources spent, priorities and meeting targets in municipalities and counties. The goal is to collect data in a co-ordinated way, and make the information flow a one time delivery per year for all steering-information needed by municipality. The number of municipalities and counties was gradually increased until the reporting year of 2001, then all municipalities were included in the KOSTRA.

Users and applications

KOSTRA provide steering information about municipalities and counties to the different interest groups, inhabitants, media, the municipality itself, different state organs and controlling authorities etc.

Equal treatment of users

Not relevant

Coherence with other statistics

The statistics is also related to other statistics like municipal residential charges , turnover from sewage and refuse activities , sewage and refuse disposal (structural business statistics) , Municipal wastewater treatment and KOSTRA - municipal water supply

Legal authority

Data are collected by Statistics Norway on behalf of the Norwegian Environment Agency with legal basis in the Pollution Control Act (13th Mars, 1981, no. 6). Statistics Norway can make use of the collected data for official statistical purposes with legal basis in the Statistics Act (16th June 1989, no. 54, §2-2).

EEA reference

Not relevant



All municipalities in Norway are covered, thus it is a complete collection (and not a survey).


Data sources and sampling

The Municipal-State-Reporting system (KOSTRA).

From 2015, the Norwegian Environment Agency also became an information source as they took over part of the electronic forms traditionally collected by KOSTRA.

Collection of data, editing and estimations

Data is collected electronically once every year, and the information should submitted to Statistics Norway by 15th of February. The Norwegian Environment Agency apply the same reporting frequency and deadlines as in KOSTRA.

The electronic forms in KOSTRA and by the Norwegian Environment Agency contain built-in consistency checks and logical tests. After arrival data are checked automatically and manually by Statistics Norway.

Unrevised data will be published on 15th of Mars. There is a second deadline on the 15th of April for municipalities to correct possible errors in the figures just published.

Data are being published on different levels, as basic data and key figures. Basic data is generally reported in absolute numbers, and will largely constitute aggregated numbers summed up for a certain period of time or at a time of year. Key figures, on the other hand, are commonly a ratio (made up of different basic data).

Calculation of statistics on country, county and KOSTRA group level (estimations)

Every year there are incidents of non-respondents, and this is visible in the statistics on municipality level as “blank data”. When it comes to figures reported in the plant level - sewage and sludge treatment –Statistics Norway make corrections in order to "neutralise" such deficiencies when calculating figures published on country, county and KOSTRA group level . Normally, this implies direct imputation of figures reported earlier i.e. if it is not reported anything in this year's reporting such missing information is collected from last year or previous years. These earlier reporting thus form the basis for the respective site when you sum up to a country, county or KOSTRA group level. The municipality in question will still come out as missing in the statistics on municipality level in that particular year, since they didn’t reported, but the statistics published for the country, county and KOSTRA group level will be subject to "statistical correction", not directly visible in the published KOSTRA figures. Thus, one can not simply sum up basic figures for all municipalities and expect that total corresponds to published national figures in the statistics. The purpose of such corrections is of course to remedy for non respondents and create more robust and reliable estimates on statistics published by Statistics Norway for the country, counties and KOSTRA groups.

Calculation of load

Due to the fact that only a minority of wastewater facilities undertake direct measures of pollution load, standard factors needs to be incorporated in the calculations. Thus, total load figures of phosphorus are largely based on this set of factors (see below for further details).

The following calculation procedure has been applied to municipal wastewater facilities, capacity of 50 pe or more:

1. If the wastewater facility provides information on load, expressed as kilogram per year, this information will be used directly.

2. If the wastewater facility provides no information, as specified in number point 1 above, but given outflow concentrations and average water quantities, then load is calculated in kilos per year from the following equation:

concentration (mg/l) x average water quantity (m3/day) x 365 / 1000

3. If measurements are not carried out, total load are calculated by multiplying the number of people connected to wastewater facilities with standard factors of average load per person per day (1.6 gram phosphorous per person per day):

number of people connected x 1.8 (g P/ day x person) x 365 / 1000

NB! For the years 2015 and earlier 1.6 g TOT-P/day x person was used as a factor instead of 1.8 as mentioned above, thus here is a “small break in time series".


Calculation of use of sewage sludge

2005 and 2006 data were reported based on gross sewage sludge and its associated percentage dry weight is now included in the reporting. In all other years dry weight of sewage sludge has been asked for. But in order to calculate the dry weight in 2005 and 2006, the information of percentage dry weight was essential, and in cases where percentage dry weight was missing, then the following method was applied to the data:

1. If percentage dry weight of the produced sludge product was reported, but not for the amounts of sludge used, then this percentage was then applied.

2. If percentage dry weight of neither the produced sludge product nor the amounts used was reported, a standard factor of 25 per cent dry weight was applied.

Calculation of age of the municipal wastewater pipelines
Calculations of the age of municipal wastewater pipelines on country level in the article - Todays Statistics - has been adjusted for pipelines of unknown age (not specified time period). Pipelines in these cases has been spread accordingly over the following time periods (1) before 1940, (2) 1940-59, (3) 1960-79 and (4) 1980 with the following percental distribution 50, 20, 20 og 10. In addition, the age presented in the article has in for some municipalities been imputated with data from earlier years if data was not avaliable from last year. These corrections constitute a few small excemptions, while the age figures in Statbank has not been corrected in this way (based solely on last years reporting and on the part of the pipelines which can be pinned down to one spesific time period).

Seasonal adjustment

Not relevant


Not relevant

Comparability over time and space

Key figures on country level and for regions (counties and KOSTRA groups) are up to 2007 based on just average calculations of reported data, while data from 2008 and later constitute statistical calculated estimates which take into consideration non responses in the dataset to a higher degree.

Comparisons over time may be reduced by the fact that some facilities have not been reported the year they first were established, but years later ("delayed reporting"). The statistics are not automatically re-calculated back in time series just because new and updated information become available. This applies primarily to smaller facilities.

Use of sewage sludge has been reported in different ways after KOSTRA took over. The 2004 reporting was carried out on aggregated municipality level, but this was changed back again to reporting on sludge treatment plant level in the 2005 data collection.

The category deposited was not included as a separate use-category in 2003 due to a ban on deposition of wet organic waste, including sewage sludge (Regulation on deposition of waste (Department of Environment 2004). Because it is not totally face out the category was re-introduced again in 2004 in order to cover these amounts in the official statistics. The changes in the reporting, in addition to that the reported data is of various quality, result in some uncertainty in the statistics.

As mentioned under chapter " Collection of data, editing and estimations" a small adjustment in methodology has taken place in the calculation of phosphorous load (TOT-P). In cases where the wastewater facility doesn’t carry out monitoring or analyse its discharges, a theoretical discharge factor of 1.8. gram TOT-P per person and day is applied. This factor however was 1.6 for the years 2015 and earlier, thus here is a small break in the overall time series of the relevant key figures and basic data published on our web sites.

Accuracy and reliability

Sources of error and uncertainty

The highest level of uncertainty is associated with possible errors and incomplete data sets as provided by the municipalities. Information on various wastewater plants and municipalities is missing, and it is sometimes difficult to detect and correct all errors or inconsistencies in the reported data set. Some uncertainty is also associated with start-up year, capacity enlargement/reduction and closing down of certain plants, which again may affect the quality of aggregated county figures. This leads to uncertainty whether the wastewater plants are still running.

Non-reporting of wastewater plants or specific parameters can lead to uncertainty in the final statistics. In certain cases, a wastewater plant not being reported can mean that the plant is closed down or that is still running but has not been reported. Therefore, continuous effort is put into removing plants shut down from the statistics in addition to adding plants that is still running but has not been reported in KOSTRA like they should.

Possible errors may occur during the revision process. It is a necessary quality-assuring tool, but errors and uncertainty may also arise as part of the process. In particular, this applies to instances where previously reported material is used as substitute for non-reported data in the current year, but also other alterations to the material during the process.

The statistics of individual wastewater treatment plants (less than 50 pe) is often less certain compared to wastewater treatment plants equal to or larger than 50 pe. Some municipalities lack total overview of small treatment plants, applying in particular to how they are distributed to type of treatment. . Thus for some municipalities these numbers may origin from "qualified guesses" and simple calculations. This may lead to uncertainty in final statistics, but at the same time is a needed task in order to generate statistics for the country as a whole.

Pay notice that certain cases of «not complying with treatment permits” in the statistics may still comply according to permit. This is due to a simplification, since the statistics does not take into consideration if the chemical analysis was taken during standard or non-standard conditions. These cases of “non-standard conditions” are usually considered extreme and chemical analysis are thus ignored. But this has not been done for the purpose of the statistics as they are considered to be few and little impact on the statistics as a whole. Temporary dispensations from treatment permits may also constitute conditions which is not always taken into consideration in the statistics. So unless Statistics Norway has been notified of any irregularities, we normally use available treatment permit information from reporting and administrative registers in the calculation.


It is Statistics Norway which carry out the quality and consistency checks to data that origin from KOSTRA electronic forms, while external data from the Norwegian Environment Agency are checked by the agency itself, but in cooperation with the county administrator ("fylkesmannen").