Water adsorbs certain trace elements from many things that it contacts on its travels. For example peat will soften water where as lime will harden it. The hardness of water is generally measured in milligrams per litre (mg/l) of calcium carbonate (caco3). Test kits are readily available from all good aquatic retailers. If your households water is very soft then when you wash your hands soap will tend to lather up easily where as with hard water it will not. Generally pond life prefer a moderate hardness level of around 200mg/l to 500mg/l
Water hardness is not normally a problem in ponds unless it is extremely high or extremely low. Certain rocks, stones, and cement within your ponds edging will raise its water hardness. Water contact with items such as peat or rain will soften your water, and any of these will also affect its pH value.