Nitrate and Sodium

Nitrate (inorganic)

The maximum acceptable concentration of nitrates in drinking water is 10 mg/L, measured as nitrogen. Nitrates are present in water (particularly ground water) as a result of decay of plant or animal material, the use of agricultural fertilizers, domestic sewage or treated wastewater contamination or geological formations containing soluble nitrogen compounds.

There is a risk that babies and small children may suffer blood related problems (methaemoglobinaemia, or blue baby syndrome) with excess nitrate intake.

The nitrate ion is not directly responsible for this condition but must first be reduced to the nitrite ion by intestinal bacteria. The nitrite reacts with the iron of haemoglobin in red blood cells which are then prevented from carrying oxygen to body tissues.

This condition appears to be restricted to susceptible infants (under 6 months of age). Older children and adults drinking the same water are unaffected. Most water-related cases of methaemoglobinaemia have been associated with the use of water containing more than 10 mg/L nitrate. In Canada, no cases of the condition have been reported where the nitrate concentration was consistently less than 10 mg/L.

Nitrite (inorganic)

The maximum acceptable concentration of nitrite in drinking water is 1 mg/L (measured as nitrogen) based as with nitrate primarily on the relationship between nitrite in water and the incidence of infantile methaemoglobinaemia. Nitrite is fairly rapidly oxidized to nitrate and is therefore seldom present in surface waters in significant concentrations. Nitrite may occur in ground water sources. If water is treated with chlorine then the nitrite will usually be oxidized to nitrate.

Where both nitrate and nitrite are present, the total (nitrate plus nitrite) concentration should not exceed 10 mg/L.

Treatment for Nitrates

Nitrates can be removed from drinking water by distillation or by reverse osmosis. Boiling does not remove nitrates and may increase nitrates in the boiled water.

Sodium in drinking water:

The aesthetic objective for sodium in drinking water is 200 mg/L. At that level it can be detected by a salty taste. Sodium is not toxic. Consumption of sodium in excess of 10,000 mg/L per day by normal adults does not result in any apparent adverse health effects. In addition, the average intake of sodium from water is only a small fraction of that consumed in a normal diet. A maximum acceptable concentration for sodium in drinking water has, therefore, not been specified. .

Persons suffering from hypertension or congestive heart disease may require a sodium restricted diet In that case, the intake of sodium from drinking water could become significant. The local Medical Officer of Health is notified when the sodium concentration in drinking water samples from systems regulated by the Ministry of Environment exceeds 20 mg/L, so that this information may be passed on to local physicians.

Softening using a domestic water softener increases the sodium level in drinking water and may contribute a significant percentage to the daily sodium intake for a consumer on a sodium restricted diet.

It is recommended that a separate unsoftened supply be retained for cooking and drinking purposes.

Sodium removal

Water that is to be consumed should be taken from a tap not connected to the water softener. Reverse osmosis is also capable of removing sodium from water. Boiling does not remove sodium and may increase sodium levels in drinking water.