In areas, where water supplies have passed through soluble carbonated rocks, like limestone, the water can be described as hard water. Hard water contains substantial amounts of dissolved calcium and magnesium. If Ca and Mg concentration reaches or exceeds the range of 80 to 100 ppm, the water hardness becomes objectionable.
Groundwater quality is highly variable. It may be nearly as pure as ideal rainwater or saltier than in the oceans. Water contamination is, however, not stable. Contaminant concentration is lowered by dilution, absorption in the permeable rock substrates, or by biological processes. The most important of natural purification processes are those biochemical changes that decompose organic compounds.


Anthropogenous interactions with water

Anthropogenous interactions with water occur in three main fields:
 household area;
 husbandry / agriculture industry
 industry.

The main sources of water pollution are:
 building activities (erosion, fertilizers, etc.);
 diary farming, agricultural activities (fertilizers, herbicides, pesticides, erosion, animal wastes concentration);
 automobile industry expansion (erosion, deicing chemicals, acid rain, other products connected with cars);
 power generation (fossil fuels – acid rain, spilling oil during transportation, warming up the wastewater, construction of the dams, spilling the radioactive materials into waterways);
 landfills (contamination of groundwater, illegal waste burial sites);
 household products (paint removers, bathroom cleansers, improper disposal of containers, washing powders);
 not existing canalization system in villages;

There are also problems as a result of a bad agricultural management in the past years:
 Extensive production of the cattle and pigs caused the total damage of soils by animal wastes in heavy concentrations;
 Overdose of chemical fertilizers;
 Agricultural lands were placed very closely to the pollution sources.


WASTE WATER TREATMENT

There are 4 main categories of wastewater and thus wastewater sewage systems:
1. Domestic sewage – wastewater from households, commercials, services, schools, administrative, etc.
2. Industrial wastewater – wastewater produced in various industrial branches, in agro-industries and forestry.
3. Municipal wastewater – sewage system, in which we cannot distinguish domestic wastewater from industrial WW; they are not in separated sewage systems
4. Rainwater – water polluted into some extent.