Indicator 6.3.2 Proportion of bodies of water with good ambient water quality

Indicator 6.3.2: Proportion of bodies of water with good ambient water quality

Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally

United Nations Environment Programme (UNEP)

Definition:

The indicator is defined as the proportion of water bodies in the country that have good ambient water quality. Ambient water quality refers to natural, untreated water in rivers, lakes and groundwaters and represents a combination of natural influences together with the impacts of all anthropogenic activities. The indicator relies on water quality data derived from in situ measurements and the analysis of samples collected from surface and groundwaters. Water quality is assessed by means of core physical and chemical parameters that reflect natural water quality related to climatological and geological factors, together with major impacts on water quality. The continuous monitoring of all surface and groundwaters is economically unfeasible and not required to sufficiently characterize the status of ambient water quality in a country. Therefore, countries select river, lake and groundwater bodies that are representative and significant for the assessment and management of water quality to monitor and report on indicator 6.3.2. The quality status of individual water bodies is classified based on the compliance of the available water quality monitoring data for the core parameters with target values defined by the country. The indicator is computed as the proportion of the number of water bodies classified as having good quality (i.e. with at least 80 % compliance) to the total number of assessed water bodies, expressed as a percentage.

Concepts:

The concepts and definitions used in the methodology have been based on existing international frameworks and glossaries (WMO, 2012) unless where indicated otherwise below.

Aquifer: Geological formation capable of storing, transmitting and yielding exploitable quantities of water.

Classification of water quality: If at least 80% of the monitoring values for prescribed parameters in a water body comply with their respective target values, the water body is classified as having a “good” water quality status. Each water body is classified as being of “good” or “not good” status.

Groundwater: Subsurface water occupying the saturated zone.

Groundwater body: A distinct volume of groundwater within an aquifer or aquifers (EU, 2000). Groundwater bodies that cross river basin district (RBD) boundaries should be divided at the boundary with each separate portion of the groundwater body being reported separately along with its respective RBD.

Lake: Inland body of standing surface water of significant extent.

Non-point-source pollution: Pollution of water bodies from dispersed sources such as fertilizers, chemicals and pesticides used in agricultural activities.

Parameter: Water quality variable or characteristic of water quality, also called a determinand.

Point source pollution: Pollution with a precisely located origin.

Pollution (of water): Introduction into water of any undesirable substance which renders the water unfit for its intended use.

Pollutant: Substance which disrupts and interferes with the equilibrium of a water system and impairs the suitability of using the water for a desired purpose.

Reservoir: Body of water, either natural or man-made, used for storage, regulation and control of water resources.

River: Large stream which serves as the natural drainage for a basin.

River basin: Geographical area having a common outlet for its surface runoff.

River basin district: Area of land, made up of one or more neighbouring river basins together with their associated groundwaters (EU, 2000).

River water body: A coherent section of a river that is discrete (does not overlap with another water body) and is significant rather than arbitrarily designated.

Stream: Flowing body of water in a natural surface channel.

Surface water: Water which flows over, or lies on, the ground surface.

Note: Indicator 6.3.2 does not include the monitoring of water quality in wetlands under monitoring level 1.

Target value: A value (or range) for any given water quality parameter that indicates the threshold for a designated water quality, such as good water quality rather than acceptable water quality.

Toxic substance: Chemical substance which can disturb the physiological functions of humans, animals and plants.

Transboundary waters: Surface or ground waters which mark, cross or are located on boundaries between two or more States; wherever transboundary waters flow directly into the sea, these transboundary waters end at a straight line across their respective mouths between points on the low-water line of the banks (UNECE, 1992).

Water quality index: The measured water quality results for all parameters combined into a numeric value for each monitoring location. These scores are then aggregated over the time of the assessment period. The index score can range between zero (worst) to 100 (best).

Percent (%): The proportion of the number of bodies of water with good water quality compared to the total number of assessed water bodies expressed as a percent.

To classify whether a water body is of “good ambient water quality” or not, a threshold is applied where 80 percent or more of monitoring values meet their target values. The number of water bodies that are classified as either good ambient water quality or not can be reported at the Reporting Basin District, and then at the national level to generate the national indicator score.

The recommended sources of data are water quality monitoring data derived from in situ measurements and the analysis of samples collected from surface and groundwaters in national or sub-national ambient water quality monitoring programmes implemented by governmental authorities. Additional water quality monitoring data from research or citizen-science monitoring programmes can be used to supplement the available authoritative monitoring data, provided they are authorised by the national reporting agency.

The number of monitoring locations required to determine the quality status of a water body depends on the type and size of the water body, but a minimum of one monitoring location per water body is required. The minimum data requirements for calculating this indicator are measurements for all of the recommended or alternative core parameters appropriate to the type of water body as defined in the methodology.

Measurements should be taken routinely, at prescribed intervals, or the same time of year each year, from the same locations. Even if new monitoring stations are introduced, data should continue to be collected from the original locations. This ensures that results are comparable between reports, thereby enabling trends to be established over time. The monitoring data needed for the indicator computation may be collected by different monitoring programmes involving different agencies and organizations. It is therefore important to establish and maintain centralized data repositories at the national level that collate the data from the various stakeholders, ensuring compatibility in reporting units between all agencies submitting data. Data should be compiled for each core parameter at each sampling location in order to calculate the indicator.

1. GEMS/Water National Focal Points in relevant Ministries, Water Authorities, National Statistical Offices etc. or their nominated representative.

The monitoring and reporting of SDG Indicator 6.3.2 requires considerable national financial and human capacities to regularly measure water quality parameters at sufficient spatial and temporal resolutions, and to consistently collect, quality-assure and process the monitoring data to compute the indicator. Substantial investments in monitoring and data management infrastructures, as well as targeted capacity development in water quality monitoring programme design and operation, will be required in many countries to enhance national capacities to regularly and consistently report on the indicator.

Recognizing the differences in monitoring and data processing capacities among countries, the indicator methodology offers a progressive monitoring approach allowing countries to start with reporting based on their existing capacity and progressively enhance the data coverage and indicator significance with increasing capacity.

Computation Method:

The indicator is computed by first classifying all assessed water bodies based on the compliance of the monitoring data collected for selected parameters at monitoring locations within the water body with parameter-specific target values:

$C_{wq}=\frac{n_c}{n_m}\times 100$

Where

$C_{wq}$ is the percentage compliance [%];

$n_c$ is the number of monitoring values in compliance with the target values;

$n_m$ is the total number of monitoring values.

A threshold value of 80% compliance is defined to classify water bodies as “good” quality. Thus, a body of water is classified as having a good quality status if at least 80% of all monitoring data from all monitoring stations within the water body comply with the respective targets.

In a second step, the classification results are used to compute the indicator as the proportion of the number of water bodies classified as having a good quality status to the total number of classified water bodies expressed in percentage:

$WBGQ\mathrm{\ }\mathrm{\ }=\mathrm{\ }\frac{n_g}{n_t}\times 100$

Where

$WBGQ\mathrm{\ }$ is the percentage of water bodies classified as having a good quality status;

$n_g$ is the number of classified water bodies classified as having a good quality status;

$n_t$ is the total number of monitored and classified water bodies.

2024-07-29

United Nations Environment Programme (UNEP)

6.3.1, 6.6.1, 14.1.1

2