Testing for alkalinity.Alkalinity measures the bicarbonate and sometimes hydroxide that make water alkaline. Bicarbonates in water come from two sources. From carbon dioxide that dissolves in water to become acidity and bicarbonate and, from the action of that acidity on carbonates for example calcium carbonate in surrounding minerals. Where there are sufficient carbonates to dissolve, the bicarbonate in the water tends to build up. Over time these waters becomes more alkaline that is, the pH rises. There is no really good or bad level of bicarbonates but they give an indication of the ability of the water to resist pH changes - the buffering capacity. In water under approximately pH 10.2, alkalinity is made up mainly by bicarbonate. Higher pH values mean that there is some hydroxide alkalinity present. For most drinking, irrigation and process water under around pH 8.3 then alkalinity can be determined by titration with acid using methyl orange indicator. If pH is above approximately 8.3 then titration using phenolphthalein indicator will give total alkalinity. For more information please see What_do_you_water_test_results_mean.doc.