Indicator 6.3.2: Proportion of bodies of water with good ambient water quality
Unlike Indicator 6.3.1, which focuses on assessing wastewater inputs, this indicator focuses on actual environmental water quality, to support Target 6.3’s call: “By 2030, improve water quality …” Indicator 6.3.2 is thus meant to assess which water bodies have “good ambient water quality” - a task that is complicated by the large number of potential water-quality parameters to be monitored (each with different implications for ecological and human health), and by the difficulty of determining what levels are acceptable for each parameter (i.e., what “good” means).
The UN approach to this conundrum has been to suggest which parameters should be monitored and reported, but let each country set their own thresholds for “good” water quality. The parameters of interest recommended by the UN for Level 1 (basic) monitoring are the following (with my own comments):
- Dissolved oxygen (DO): This is a good choice because it is relatively easy to measure and interpret and is critical to aquatic organisms.
- pH: This is easy to measure, and could potentially capture serious pollution issues, such as discharge of alkaline tannery wastewaters or highly-acidic industrial wastes.
- Conductivity: This is easy to measure, and could potentially identify high-salinity discharges. But water bodies vary naturally in their conductivity, so the only way to have a threshold value would be to have separate categories for freshwater, brackish water, and saltwater.
- Nutrients (N and P): These are somewhat harder to measure. They can provide useful information on trophic status, although given that DO is being measured, their added value is less clear. More importantly, it is notoriously hard to set thresholds of acceptable concentrations for nutrients, given the large range in natural nutrient loading and the differential sensitivity of different ecosystems to eutrophication problems. On the other hand, increasing awareness of the health effects of NO3- in drinking water (and the ubiquity of NO3- as an agricultural pollutant) justify a focus on that form of nitrogen in particular.
Obvious gaps in these recommended parameters include some measure of microbial contamination (e.g., E. coli), some measure of toxicity, and some form of direct monitoring of aquatic organisms (biomonitoring). The UN recommends these as options for Level 2 monitoring as countries are able.
