Water abstraction is divided into two categories - fresh and non-fresh water.
Fresh water: to surface water are allocated water on land (including the Danube river), and to the groundwater - all water which is below the surface of the ground in the saturation zone and in direct contact with the earth layers.
Non-fresh water: are the sea and transitional waters. Since 2006 only sea water is included to non-fresh waters as according to the Classification for characterization of surface types' water bodies under the Water Framework Directive, transitional waters are not identified in Bulgaria.
Water supply categories: Self-supply; Public water supply, Irrigation systems and other supply: (raw and reused/ wastewater received from other users).
Gross water abstraction is a sum of fresh water abstracted for distribution and self-supply of the enterprises. Water for production of hydroelectricity is a separate category and not included in the total abstraction. Self-supply of households is not covered.
Returned water: The water abstracted from any fresh water source and discharged back into it without use (primarily at mining and quarrying, and construction activities).
Fresh water net abstraction: the fresh water gross abstraction minus returned water.
Water used is a sum of water used by the categories of supply:
Water losses are formed from physical losses in the transport of water, irregular use, errors in measurements, etc. The volume of losses is aggregated for a group of operators in order to avoid the double counting. On RBD level water losses are calculated using a regionalizing factor "supplied water". It is assumed that water losses in self water supply are negligible.
Water generated from point sources: water, which after use leaves the place of use and is discharged into the public sewerage and water bodies. Data is collected through statistical survey on water use, covering more significant water users. Wastewater generated by the households is result from data reported by public water works and estimation. Two categories are distinguished - wastewater and water from cooling processes.
Wastewater discharged after treatment: Amount of wastewater discharged from wastewater treatment plants of the enterprises and UWWTP (according to the latest level of treatment). Wastewater of households with own/independent treatment is also considered as treated.
Water discharged into water bodies: a sum of water discharged by the surveyed enterprises, public sewerage/UWWTP and households with own/independent treatment.
Collected wastewater into public sewerage: calculations are based on data reported by the Public water works and estimations. The quantities from non-point sources (rain-off, drainage and other unallocated water) are also included.
Urban wastewater treatment plants (UWWTP): covered are all operating plants treating wastewater from settlements. Wastewater treatment plants at enterprises, hotels, etc. are referred to a separate category. Design capacity BOD5 (tons O2/day): maximum flows and loads of the influent the facilities are designed for, which conform with the fixed standards.
Public water supply and sewage network - data refer to the network operated by public water supply operators. Also is included the sewage network of municipalities with organized discharge of wastewater in urban wastewater treatment plants.
Population connected to public water supply/public sewerage and UWWTP - data are the result of survey "Water supply and sewage". It is possible to overestimate the population in settlements with partially build water supply /sewage network, at which only a part of households is connected. Population with independent own wastewater treatment (via septic tanks, cesspools, etc.) is calculated as a difference between the total population and population with a public sewage system.
Measuring water qualities: they are reported by the respondents through water meters, and in case of their absence - using the capacity of the pumps, multiplied by the time of their work; energy consumption of pumps, specific factor, etc.