[en] The hydro- and hydrogeological processes, and the identification of pollution sources and pathways can all be studied by examining the stable isotope composition of water molecules [δ²H(H²O) and δ¹⁸O(H₂O)], the solutes in water [δ¹⁵N(NO₃), δ¹⁸O(NO₃), δ³⁴S(SO₄), δ¹⁸O(SO₄), δ¹³C(DIC)] or the particulate organic matter [δ13C(POM) and δ¹⁵N(POM)], together with the major ion concentration in water such as Na⁺, Ca₂⁺, Cl^-, SO₄^2-, NO₃^- and NH₄⁺. Basic hydrochemistry methods are important for identification of pollution levels but the stable isotope methods are critical for calculation of evaporation, evapo-concentration, source identification, and for untangling water budgets from pollution budgets. Techniques that combine hydrochemical and stable isotope methods have therefore become essential tools for identification of non-particulate, non-source agricultural pollutants. The major advantages of these combined techniques are their relatively low cost and their high success rates, even when used in areas lacking long term monitoring and baseline data.