This part of ISO 15587 specifies a method for extracting trace elements from a water sample using nitric acid as a digestion agent. The method is applicable to all types of waters with a suspended solids concentration of less than 20 g/l and a total organic carbon (TOC) concentration expressed as carbon of less than 5 g/l. The nitric acid digestion method is empirical and it might not necessarily release elements completely. However, for most environmental applications the result is fit for purpose. Nitric acid digestion is suitable for the release of: Al*, As, B, Ba*, Be*, Ca, Cd, Co, Cr*, Cu, Fe*, Hg, K, Mg*, Mn, Mo, Na, Ni, P, Pb, Se, Sr, Tl, V*, Zn (asterisk indicates a possible lower recovery compared to aqua regia digestion method specified in ISO 15587-1, see reference [1]). It is suitable for the release of Ag only if the sample is stabilized immediately after digestion. Nitric acid digestion is not suitable for Sb, Sn and for the digestion of refractory compounds such as SiO2, TiO2 and Al2O3. The method is generic and may be implemented using a wide variety of equipment provided — the digestion composition is unchanged, — the digestion temperature is known, and — the digestion duration is in accordance with this temperature.