We often get questions about the hardness of drinking water, the amount of salt you should add to your dishwasher, fluoride in our water – and even the quality of our water. Here are some general points to consider.
How hard is the drinking water?
Hardness is the sum of the harmless calcium and magnesium ions in the drinking water. Hard water – which has more that about 80 - 100 milligrams per litre (mg/l) hardness expressed as CaCO3 (calcium carbonate) – can cause scale deposits in pipes and kettles or irons.
Soft water has less than 100 mg/l hardness as CaCO3. While soft water is better to wash with because it lathers better, it can be corrosive to pipes.
There is also a theory that soft water causes high blood pressure in some people, which means it should only be used for washing and not for drinking purposes.
Water supply in most areas of Pretoria is in the region of 80-100 mg/litre. However those areas which are getting fountain or borehole water have a hardness of between 120 - 180 mg/litre CaCO3.
What is the white precipitate in my kettle?
As mentioned, this is the calcium carbonate present in drinking water. The water has high calcium content and when the water is heated, the calcium becomes insoluble and precipitates on the element. This is not harmful to your health in any way; the kettle should just be cleaned on a regular basis.
Is Tshwane water safe to drink from the tap?
Yes, it is. High-quality tap water is available almost everywhere, and we’ve treated it to be free from harmful micro organisms and chemical contaminants. Therefore, it is safe to drink water straight from the tap.
Is bottled water safer than tap water?
No. There is no assurance that just because water comes from a bottle it is any cleaner or safer than water from a tap. There is no need to buy bottled water since the City of Tshwane's water has been tested and conforms to the specifications set by the SABS for drinking water. This ensures that the water is suitable for lifetime consumption without any ill effects.
Are minerals added to the tap water?
Many of the substances present in your drinking water occur naturally in the water. These are elements like calcium, iron, zinc, potassium and sulphates. Chlorine is added to get rid of harmful organisms.
Why does the water in the tap water sometimes have an earthy smell?
During summer algae grows easily in raw water and releases eosin, a harmless compound not removed by conventional purification, which has an earthy smell. When it reaches a certain level, the City of Tshwane uses activated carbon to remove the smell.
Why does the water in the tap sometimes have a reddish brown appearance?
Generally, slight colour changes do not indicate a serious water problem. The water may have a reddish brown appearance caused by iron salts due to the corrosion of steel pipes and valves. The colour could also be due to repairs on the water mains and this usually disappears after 24 hours.
Is tap water free from cholera?
Tap water supplied by the City of Tshwane is free from cholera and safe to drink. However, do not drink water from rivers, streams and dams as they are opened to contamination.
Is tap water suitable for mixing infant formula?
Tap water is suitable for use in infant formula. There is no evidence to prove that tap water needs to be retreated for mixing infant formula.
What do I do in an emergency when I am not sure of the quality of the tap water?
To prevent traveller’s diarrhoea, boil the water for a minimum of three minutes. This will kill the bacteria that cause diarrhoea. However, the mineral composition of the water may also cause problems, don’t use the water for a long time without getting it tested first.
How much salt do I add to my dishwasher?
Although hard water is healthy to drink, it makes washing dishes difficult as it forms a scum layer on the water surface. Dishwashers therefore use water softeners, which replace the calcium and magnesium ions with sodium ions, which make the water soft. The sodium comes from the salt that you add to the dishwasher.
To find out how much salt you need to add you must convert the hardness in milligrams per litre (mg/l) to the units used in the manual provided by the manufacturer. These units are usually French or German degrees of hardness or in mmol/l alkaline earth ions.
• 1 mg/l CaCO3 = 0.056 German degrees
• 1 mg/l CaCO3 = 0.10 French degrees
• 1 mg/l CaCO3 = 0.01 mmol/l alkaline earth ions.
For example, if the water has a hardness of 80 mg/l CaCO3, convert this to German degrees by multiplying 80 by 0.056 = 4.48 German degrees. If the manual gives the hardness as French degrees multiply 80 by 0.10 to get to French degrees = 8. To convert to mmol/l multiply 80 by 0.01 = 0.8mmol/l.
Once you have the hardness in the correct units, consult the manufacturers' manual to find out the amount of salt required.
Fast fluoride facts
Fluoride is a highly electro-negative element and is an essential trace element in a normal diet. The body uses it to strengthen the enamel of the teeth by binding to the calcium in the teeth, which prevents caries.
In the US it was found that fluoride levels of 1 mg/l reduced dental caries by 50 percent. This process occurs from birth until the permanent teeth have been formed (at about eight years of age) and the effect is lifelong.
Fluoride concentrations of 0.5 mg/l are considered to be minimum concentration that can protect against dental caries, while 1.0 mg/l of fluoride can cause mild dental fluorosis (staining of teeth)
Fluoride occurs naturally in water (about 0.1 - 0.3 mg/l) and can be found in higher concentrations in groundwater (up to 12 mg/l).
Fluoride – which has no taste smell or colour, even at high concentrations – can also be found in tea, vegetables meat and fish.
Too much fluoride (concentrations above 3 mg/l) can damage the skeleton (skeletal fluorosis), depressed thyroid activity, kidney damage and interference with the immune system. Acute poisoning causes vomiting, abdominal pain and diarrhoea.
Presently the fluoride content of the piped water supply in Pretoria is 0.18 - 0.2 mg/l. The City of Tshwane does not add fluoride to the water.
Sweden, Belgium, the Netherlands, West Germany and Hungary have discontinued fluoridation of the water supply. Austria, Greece, Denmark, France and Italy have never introduced fluoridation.