The pollution levels in rainwater are made up of a number ofpollutants, inorganic pollutants, metals, organic pollutants and microbialpollutants (Meric, 2016).Rainwater is the purest water found naturally, and contains a wide range ofions and cations (N.F.
Gray, 2008)When speaking about inorganic pollutants the main issues arepH and minerals, the mean pH of rainwater is in the acidic range. The acidityof rainwater naturally is taken as 5.6 (Meric, 2016).At a pH level of 6.
0 or less freshwater shrimp cannot survive, at pH level 5.5,bottom dwelling bacterial composers cannot survive and begin to die, causingnon-decomposed leaf litter to lie on the bottom and deprive plankton of foodsupply (Meric, 2016).Acidic rain happens when acidic pollutants, sulfur dioxide (SO2),and nitrogen oxide (NOx) precipitate in the form of rain (Meric, 2016). The high values of trace metals (Fe, Al, Cu, Zn, Pb, Cd) inrainwater samples are due to long-range atmospheric transport of anthropogenicactivities, these include industrial activity, coal combustion and automobileexhaust fumes (Meric, 2016).These elements are responsible for the catalytic activity of rainwater.
Organic compounds are present in the gas and aerosol phase,both the processes of gas and particle scavenging are important paths ofatmospheric deposition of these compounds (Meric, 2016).In rainwater samples the concentration of organic pollutants can vary considerablydue to seasonal transport of the radionuclides, the highest activityconcentrations are in the winter months and are due to the wind direction (Meric, 2016). Natural fires andvolcanic eruptions are the major natural sources of polycyclic aromatichydrocarbons. Many processes can be considered as the source: industrialemissions from catalytic cracking, automobile exhaust emissions and tyredegradation (Meric, 2016).Pesticides are a group of organic pollutants which reach the atmosphere throughthree main pathways: volatilization during and after application, transport ofsoil particles and dust loaded with pesticides, and losses during pesticidemanufacturing processes (Meric, 2016)Microbial pollution is a major sourceof pollution into our water systems, particularly in water reuse plants.
Pathogens are found primarily in the faeces of birds and mammals that haveaccess to the water reservoir.