The standard applies to all types of water with a pH between 4.0 and 9.5 within a temperature range of 0 to 50 °C. Special precautions must be taken with samples with low ionic strength and/or buffer capacity. Indications are given for less accurate measurements below pH = 4.0 and above pH = 9.5 at temperatures up to 100 °C and in colloidal solutions and suspensions.