The subdivision of still waters in Flanders has been drawn up by Haskoning-Belgium. Starting point are two basic aspects of water quality, viz. ion-composition and nutrient-composition. The ion-composition is the sum of all the dissolved ions in the water. The nutrient-composition only takes into account nitrogen and phosphorus-containing ions. Three categories are discerned: (1) brackish water (Na and Cl are the dominant ions), (2) nutrient-poor freshwater (ranging from non-buffered acid water (rain water) to highly-buffered (containing groundwater), (3) very nutrient-rich water.