1. Water Chemistry: Hardness

2. Hardness Related to the dissolved minerals in contains
General Hardness (GH): caused be divalent ions (valence of two, can form 2 covalent bonds)
Calcium and Magnesium
Carbonate Hardness (KH): due to carbonate/bicarbonate ions
Main buffering capacity
High KH, stable pH
Low KH, unstable pH

3. Hardness
Calcium and Magnesium acquired in aquatic environments through contact with rocks and sediments
Positive Ions
Bicarbonate and Carbonate acquired from limestone sediments and carbon dioxide
Negative ions

4. Hardness
Carbon dioxide reacts with water to form carbonic acid (1) which at ordinary environmental pH exists mostly as bicarbonate ion (2). Microscopic marine organisms take this up as carbonate (4) to form calcite skeletons which, over millions of years, have built up extensive limestone deposits. Groundwaters, made slightly acidic by CO2 (both that absorbed from the air and from the respiration of soil bacteria) dissolve the limestone (3), thereby acquiring calcium and bicarbonate ions and becoming "hard". If the HCO3– concentration is sufficiently great, the combination of processes (2) and (4) causes calcium carbonate ("lime scale") to precipitate out on surfaces such as the insides of pipes. (Calcium bicarbonate itself does not form a solid, but always precipitates as CaCO3.)

5. Hardness
Water Hardness is read as parts per million (ppm) or weight/volume (mg/L) of calcium carbonate in the water
Hard water (higher concentration): toothpaste is gritty when brushing (not as much lather), harder to get soap off
Soft water (lower concentration): toothpaste is smooth and lathers easily, soap rinses off easily