ferskvanns

Ferskvann, in hydrological terms, refers to water with low concentrations of dissolved salts. It is distinguished from seawater by salinity levels typically well under 1 g/L, though exact thresholds vary by discipline. In Norwegian usage, ferskvann translates to freshwater and covers non-saline water bodies such as rivers, lakes, wetlands, and groundwater.

Freshwater occurs in surface forms—lakes, rivers, streams, and wetlands—and in groundwater, which supplies a large share of drinking water in many regions. Globally, about 2.5–3% of Earth's water is freshwater, with the majority stored as ice and deep groundwater, leaving a comparatively small portion accessible for human use.

Freshwater ecosystems are organized into lentic systems (lakes and ponds) and lotic systems (rivers and streams), as well as wetlands and springs. They support a wide range of organisms adapted to variable conditions, including oxygen fluctuations, nutrient availability, and temperature changes. Biodiversity in freshwater habitats underpins fisheries, nutrient cycling, water purification, and insect populations that feed higher trophic levels.

The chemistry and physics of freshwater are shaped by catchment characteristics, precipitation, evaporation, and human inputs. Dissolved oxygen, pH, nutrients, and turbidity influence productivity and habitat suitability. Climate change, pollution, habitat alteration, invasive species, and over-extraction threaten freshwater systems, reducing water quality and degrading ecological integrity.

Humans rely on freshwater for drinking water, agriculture, industry, energy, and recreation. Sustainable management includes protecting watersheds, reducing nutrient runoff, restoring wetlands, regulating withdrawals, and improving wastewater treatment. Effective stewardship aims to balance ecological health with social and economic needs.