ISO 10523:2008 specifies a method for determining the pH value in rain, drinking and mineral waters, bathing waters, surface and ground waters, as well as municipal and industrial waste waters, and liquid sludge, within the range pH 2 to pH 12 with an ionic strength below I = 0,3 mol/kg (conductivity at 25 ï¿1/2C <2 000 mS/m) solvent and in the temperature range 0 ï¿1/2C to 50 ï¿1/2C.