Every wondered why the ring forms around the bath? Why the porcelain hand basin looks like it always needs cleaning? Why your hair feels dirty even when it has just been washed? There's a good reason for those outcomes and the cause is related to the chemistry of the water.
Let's start with soft water, then work our way to understanding the term 'hard water' and what it means to us.
Rainwater is not pure water because it has the gases and a range of other particles in the atmosphere dissolved in it, which may include sea spray from the oceans, nitrate from the electrical activity of lightning (nitrogen gas converted to nitrate), nitrogen and sulphur gases from pollution, dust, pollens, bacteria and numerous other compounds. Compared to water that has run over the ground, rainwater is reasonably clean. But you need to collect it without making it any more contaminated and therein lies a problem.
So rainwater essentially is water with some minor impurities, with an electrical conductivity (EC) less than 0.01 dS/m and a pH about 4.5 to 5.5 (that's slightly acid). Close to industrial areas, the rain may be more acid (lower pH) and can cause serious environmental problems.
Now let the rain fall on your roof. What sort of roof is it? Concrete tiles, terracotta tiles, galvanised iron, Zincalume sheeting, anodised aluminium, timber, fibrous cement, asbestos cement, lead flashings, a chimney from a wood fire, a TV aerial that is a great perch for resting birds, gutters that accumulate leaves and decay to form beaut compost? Think about it! How clean is your roof? Well, whatever is on the roof may end up in your rainwater tank and the chemicals will contaminate the water with both organic and inorganic components.
So the EC will be elevated a little, but probably still less than 0.05 dS/m and a pH a little higher around 5-6.
For the story on water hardness, we need to consider only calcium and magnesium. Hardness is an aesthetic quality of water that is used to describe the ease with which soap forms a lather. We can drink extremely hard water but it may not make a good cup of tea or coffee.
In soft water, ordinary soap lathers quickly and easily, and the soap is easy to rinse out of clothes in the laundry or from your hair and skin under the shower. Your hair feels clean and not 'clingy'.
A problem with very soft water is that because of its purity, the copper pipes used in the house will start to dissolve in the water. The green mark on the porcelain under the dripping tap is an accumulation of copper from the pipes. The cleaner the water the more corrosive it is.
In the bath or shower, soap is difficult to get a lather with hardwater and instead of feeling slippery it seems difficult to wash. Your hair, in particular, starts to matt together and it's difficult to run your fingers through your wet hair. When your hair dries it feels sticky and clings together because the calcium and magnesium compounds have not been removed from the hair fibres but are acting like glues. Your skin may be clammy because the calcium/magnesium precipitate absorbs moisture, and may also leave the skin drier than usual.
In the bath, there are tell-tale signs of the high water mark and the hand basin gets a greasy film over the surface of the porcelain. It requires cleaning with some of the special products because this scum is insoluble in water. Shower screens and tiles get a matt appearance (dull) and appear to have a coating that will increase in thickness over time, unless removed. It is usual to use a proprietary product to remove this 'grunge'. These products are usually acidic to dissolve the calcium and magnesium precipitate.
Inside pipe, hard water leaves an insoluble deposit of calcium and magnesium carbonates and over time may completely clog up the pipe. In hot water services, in the electric kettle or coffee making machines, the calcium deposits on the heating element and can build up to a stage that the water is no longer in contact with the element, the element overheats and explodes.
HOW DO WE MEASURE HARDNESS
Some imported water softeners refer to hardness in obsolete German units of "degrees of hardness" (odH). To convert odH to total hardness in mg/L CaCO3, divide by 0.14. See references to other units at http://en.wikipedia.org/wiki/Hard_water)
CLASSIFICATION OF TOTAL
Soft < 60 mg/L CaCO3
Other classification systems are intermediate to the Australian Drinking Water Guidelines (2004)and refer to various scales of total hardness as:
<17 mg/L CaCO3
Obtain a copy of the Australian Drinking Water Guidelines at http://www.nhmrc.gov.au/publications/synopses/eh19syn.htm
DRINKING WATER SUPPLIES
In 1998, I measured 43 town water supplies across coastal and inland NSW as part of a research project. The hardness in the water supplies was extremely variable but noticeable different between the coastal fringe and the inland (west of the Great Dividing Range). Figure H1 shows the number of towns (frequency distribution) for a range of total hardness. It is clear that inland water supplies are harder than coastal supplies. As a comparison, rainwater has a hardness of less than 5 mg/L.
Metropolitan Water Supplies
|Metropolitan Supply||Total Hardness (mg/L CaCO3)||Source of Data|
|Melbourne - City West Water||15-29 mg/L||(City West Water, 2007)|
|Melbourne||10-26 mg/L||(Melbourne Water 2006)|
|Sydney’s water||51-65 mg/L||(Sydney Water 2005)|
|Brisbane||106-143 mg/L from Mt Crosby||(BCC, 2008)|
|Brisbane||89-97 mg/L from North Pine||(BCC, 2008)|
|Adelaide||80-157 mg/L Metropolitan Adelaide||(SA Water, 2008)|
|Adelaide||81-140 mg/L from Hope Valley||(SA Water, 2008)|
Brisbane City Council reports on the average hardness of Brisbane's water as 68-210 mg/L CaCO3) - see the website for more details. http://www.urbanutilities.com.au/ckfinder/userfiles/files/DW%20Quality%20Data%20-%20Internet%20July2008jun2009v4final.pdf
EFFECTS OF HARDNESS ON SOAPS AND
|The problem that hardness causes to our use of water for washing (persons and clothes) is that the calcium and magnesium salts react with the surfactant (the surface active agent) and reduce its effectiveness. We can overcome that problem by using more washing soap to bind the calcium and magnesium. Additional amounts of washing soda (sodium carbonate) or borax can be used to precipitate the calcium and magnesium. The problem with soaps in hard water is that the compounds formed with the soap result in a greasy curd that is insoluble in water and difficult to wash out. It doesn't matter how much extra soap we use, the curd remains insoluble.
So if we have to learn to live with hard water, how do we overcome the effects of the hardness. SIMPLE - use a high quality detergent. The harder the water, the more detergent you use. Phosphates have been added to water to deal with hardness and these salts are very good at combining with calcium and magnesium and keeping them in suspension so that they can be effectively washed out of the clothes. Whether substitutes for phosphorus, such as zeolites work in hard water may need to be tried.
The third way of dealing with hard water is to pass the water through a softener.
These devices are ion exchange systems - that is, they exchange sodium ions for calcium and magnesium ions. Water passes through a softener, usually a large tank something like a LPG gas bottle. On its way through the media inside the softener, the calcium and magnesium ions are captured by the media and a replacement occurs. Sodium ions on the media are displaced by the calcium and magnesium. Instead of the water having say 100 mg/L (parts per million) of calcium and magnesium combined, the softened water now has very low levels of calcium and magnesium, but levels of sodium displaced are fractionally higher than the combined calcium and magnesium displaced. At regular intervals, the ion exchanger has to be replenished, that is back flushed with a brine solution (concentrated sodium chloride solution) to replace the calcium and magnesium so the process can start again. The backwash should be discharged to sewer and not onto the ground or into a septic tank (or other on-site system). The period between backwash events will depend upon the hardness of the water and the volume of water treated. Check with your irrigation specialist for the correct sizing of a water softener.
Reverse Osmosis (RO) is the removal of contaminants from water by forcing the water through a semi-permeable membrane. These devices produce very clean water, but are expensive to operate and waste about 90% of the water passing through them. RO water is 'too pure' to drink.
If you have other questions that you think the answers may help other, please email me and let me know. I cannot guarantee that I will be able to list all the information we require to use laundry and other household products in a responsible way. email firstname.lastname@example.org
References: City West Water-Melbourne:
Sydney Water: http://www.sydneywater.com.au/Publications/Reports/TypicalWaterAnalysis.pdf#Page=1
Brisbane Water: http://www.brisbane.qld.gov.au/BCCWR/LIB169/june2008_CHEMICAL_ANALYSIS_WATER_QUALITY_RESULTS.PDF (Mt Crosby and North Pine supplies, June 2008
Adelaide Water: http://www.sawater.com.au/nr/rdonlyres/f4353c40-f966-4493-9cd1-7a14f87c8e2f/0/dwqr_0708.pdf