Water hardness - South West Water

Water hardness
Rain water is naturally soft but when it passes through rocks, such
as chalk and limestone, it picks up minerals. These dissolved
minerals are normally calcium or magnesium compounds and they
give water its hard nature.
Are there hard water areas within the south west?
The majority of our customers’ drinking water supply is sourced from
surface waters, such as moorland rivers and reservoirs. This water is
classified as either soft or moderately soft.
East Devon is the only area in our region where the water supply is
considered slightly hard or moderately hard. This is because the supply
is derived from boreholes drilled deep underground.
Hard water can lead to the formation of scale inside kettles, irons and
washing machines, sometimes referred to as limescale. It can also make
it more difficult to form lather from soap, washing up liquid and washing
powders. The map below shows the hardness of water in each area of
the south west.
Relevant facts:
Some hardness can be
removed by boiling. This forces
calcium carbonate out of
solution to produce a deposit of
Most of South West Water’s
customers need only use the
lower amounts of washing
powders specified by
Due to the lack of hardness,
scale formation inside waterfed appliances should not be
a problem for the vast majority
of our region.
The vast majority of customers
will not need to use salt
tablets in their dishwasher;
we advise trying without salt.
Please refer to the ‘water
hardness’ chart, left, for more
as calcium
as calcium
0 – 20
0 – 50
Moderately Soft
20 – 40
50 – 100
Slightly Hard
40 – 60
100 – 150
Moderately Hard
60 – 80
150 – 200
80 - 120
200 – 300
Very Hard
Over 120
Over 300
*mg/l = milligrams per litre = 1 part per million
as English
0 – 3.5
3.5 – 7
7 – 10.5
10.5 – 14
14 – 21
Over 21
as French
0- 5
5 – 10
10 – 15
15 – 20
20 – 30
Over 30
Hardness as
0 – 2.8
2.8 – 5.6
5.6 – 8.4
8.4 – 11.2
11.2 – 16.8
Over 16.8
Customer services helpline: 0800 169 1144, Minicom: 0800 169 9965
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Do I need to install a softener?
Some customers living in harder water areas choose to install water
softeners. We recommend that customers do not soften the water supply
to the taps from which drinking water is drawn. Some softeners can
increase the levels of sodium in the water which is harmful for people
suffering from high blood pressure. Softened water can be more
corrosive to metal pipe work and thereby increase the concentration of
metals in the water.
In hard water areas, how can the build up of scale be prevented?
Fresh water should always be used to fill kettles - re-boiling water will
encourage the build up of scale and other deposits and can lead to a
change in the taste of the water.
To help prevent the build up of scale in boilers and central heating
systems, it is good practice to keep the temperature setting below 600C.
The formation of scale is very slight until the temperature of water
reaches 710C and 600C is normally sufficient for domestic purposes.
If you have any further queries regarding water quality or require further
information, please contact us on the freephone number below.
Customer services helpline: 0800 169 1144, Minicom: 0800 169 9965
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