| 1 | Accessible Water | is the quantities of surface and groundwater or both that is accessible to everyone. |
| 2 | Salt Water | is the one contains large amounts of dissolved salts such as sodium; this can be found in world's oceans and seas. |
| 3 | Fresh Water | it does not contain significant levels of dissolved minerals or salt, this can be found in springs or rivers. |
| 4 | Desalinated Water | is the one that are desalinated to become fresh water suitable for use. |
| 5 | Surface Water | All the freshwater and saltwater which come into direct contact with air, such as oceans, lakes and rivers water. |
| 6 | Groundwater | rain water that is infiltrating into the underneath surface layers of the Earth. |
| 7 | Agricultural Wastewater | is the wastewater residuals resulting from agricultural uses and wastewater. It is often saturated with salts and producing toxic wastes resulting from the use of fertilizers and pesticides. |
| 8 | Wastewater | is the residuals result from uses of household and public utilities. |
| 9 | Gray Water | is the outcome of the used water, except of toilets water. It is namely hand-washing basins, showering, clothes washing, dishwashers and kitchens water ..etc. |
| 10 | Black Water | is the water generated from the use of latrines which contain large amounts of organic pollutants resulting from human excreta. |
| 11 | Treatment of Water | a group of natural, chemical and biological processes which eliminates solids, and organic materials and micro-organisms, or reduce it to acceptable degrees. This may include eliminating some nutrients with high concentrations such as phosphorus and nitrogen. |
| 12 | Pre-treatment | includes insulation and cutting down large pieces present in water to protect the plant parts and to prevent clogging the pipes. This process removes 5-10% of the biodegradable organic materials as well as 2-20% of suspended solids. These percentages are not considered sufficient for the purpose of reusing water for any activity. |
| 13 | Primary Treatment | eliminating the organic material and inorganic removable solids ones by sedimentation. At this phase, 35-50% of the organic biodegradable materials, as well as 50-70% of suspended solids can be eliminated. Even though, these percentages are deemed not sufficient to make water fit for use. |
| 14 | Secondary Treatment | At this phase, the organic materials are bio-transformed into bio-blocks that are eliminated later by sedimentation in the secondary sedimentation basin. Secondary treatment can eliminate approximately 90% of the biodegradable materials as well as 85% of suspended solids. |
| 15 | Advanced Treatment | This phase of treatment is applied if there is a need for pure water with a high quality. It consists of different processes to remove contaminants that cannot be removed by the aforesaid conventional means. Nitrogen, phosphorus, organic materials, suspended solids, the materials that are difficult to analyze easily and toxic substances are example of pollutants. |