Contamination is the only issue, that can be due to lack of cleaned piped supply, ground water contamination due to septic tanks and soppits, discharge of untreated wastewater into surface water streams. Improper drainage facilities in various cities. But these are mostly issues that third world is facing.

Dear Ramachandra

In Brazil , the ANA ( National Water Agency ) helps keep PNQA ( National Assessment Program Water Quality ) implemented to meet the needs of water quality monitoring program in the country , one of the main issues of water resources management in Brazil.

However the quality of our water runs into geographic gaps whose regions are still not surveyed , and the lack of funds and resources to this sector . There is also a lack of standardization of research and information for the collection and laboratory analysis between the different regions of Brazil .

According to recent research conducted by the core medical UFMT ( Federal University of Mato Grosso ) , Brazilian drinking water may be the presence of 22 different types of pesticides , heavy metals 13 , 13 solvents and 6 disinfectants . Physicians guide to the presence of these substances is tolerated to a certain level of concentration in the human body , however, these levels are violated for economic convenience in industrial and agricultural production .

The European Union , for example , admits only the presence of five pesticides in low concentrations in drinking water . In Brazil , traditionally control the quality of our drinking water was always on the elimination of bacteria , disregarding the real risk of chemical contamination .

In March 2013 , the Ministry of Health reported that only 67 % of Brazilian cities have methods to monitor and evaluate the quality of Brazilian water, the government has since gone on to work with the goal to increase that percentage to 75 % in 2015.

The monitoring covers the work of control, registration and surveillance of water sources of supplies and services . Also in Brazil , there is a great need to increase the quality in drinking water distribution , improving the coverage and quality of per capita access .

Sources:
 
 http://www2.ana.gov.br/Paginas/projetos/QualidadeAgua.aspx http://www.jb.com.br/ciencia-e-tecnologia/noticias/2011/07/25/controle-da-qualidade-da-agua-no-brasil-nao-acompanha-contaminacao-quimica/

House-hold waste or waste from human constructions not cleaned up can contaminate open-access water sources. Perhaps some people contaminate open-access water to remove organisms depending on it (e.g. mosquitoes potentially transmitting diseases, amphibians, like frogs, making a lot of noise close to housing so that people cannot sleep, etc...)

Thus all water bodies next to huge cities?

It is all about source pollution of water which is standard. What about corroded material and secondary pollutants when source water pollutants interact with supply pipes etc. Further, in developing countries where it is common that leakage from sewer pipes enters into water supply pipes etc.

Chemical pollution isn't the only factor to affect water quality. Sediments, runoff and erosion are three natural ways that water can be compromised. Temperature pollution affects the quality of plant and animal life outdoors, as do oxygen levels. Decaying natural materials can taint a water supply, as can pesticides, detergents, greases, oils, and garbage.

Water pollution occurs at three points in a urban supply:

1. At Source

2. During transfer (or pipeline)

3. At storage (pumping station or domestic storage)

At source, heavy metal (like Arsenic, lead etc.) contamination is the most severe problem. other is fluoride etc. This type of pollution mostly caused by the geology of the area.

Poor quality of pipelines and maintenance cause contamination of water during transfer and storage..

water pollution in cities is becoming an increasingly serious issue. The most prevalent form of contamination is from sewage and grey water. Other then these common sources, The heavy metal contamination due to various industrial activities, pharmaceutical including radioactive waste from waste water treatment plants. There are many more sources like corrosion in piped supply, bio fouling and bacteriological wastes.

And concerning pharmaceutical waste, many are culminating in each individual body to be released in nature. Many water bodies contain traces of pharmaceutical molecules or not?

@Marcel Pharmaceutical waste are becoming very important issue it has been observed that pharmaceutical waste usually pass through waste water treatment plants and they exist in the marine environment/river/waterbody.

Cities, towns and other settlements have a major effect on water quality because of the sheer number of people living there. Kerbing and stormwater outlets collect water that runs along streets, down the drains and into the rivers and sea.

Everything that is thrown on the roadside can end up in the stormwater system and be washed into streams to affect water quality. Pollution can also filter through the ground into groundwater.

Cars and trucks on the road or parked in car parks can drip oil and fuel in small amounts. When it rains these oil drips are washed into the stormwater drains. People cleaning their cars often allow the suds from their washing liquid to wash into the drains. Some people even throw left-over paint or engine oil down drains without thinking about where this poisonous brew will end up.

While each single incident may seem a small amount of waste, the sheer number of people living in cities combines to create a major effect on water quality. Wrappers from fast food outlets are one of the major sources of litter in city streets, all of which can be washed down into drains.

Sewerage systems and rubbish dumps are also factors in water quality. Large populations put pressure on the ability of systems to dispose of waste without affecting the environment.

@Jeremiah

I fully agree that the small individual impacts are multiplied by thousands/millions in (very) big cities.

Most important factor affect the water quality in city is domestic waste.

Second population increasing population leads more domestic waste

then un wanted factory waste water its also play an important role in water quality

Usually there are two sources of water supply in city (1) surface water (2 ) ground water. Surface water mainly contaminated by defective drainage system, industrial waste water, Rain water which is the main source of water is directly contaminated by various factors. In which bacteriological pollution has great impact. Defective pipe transport line also impact up to great extent. Where as groundwater is very much influenced by geological strata. Water rock interaction cause for many type of contamination for example Fluoride, Arsenic toxic elements etc. Application of fertilizer, insecticide and pesticide on agriculture and horticulture etc also create problem like nitrate and various other pollution in water. In addition to this Anthropogenic pollution may have direct influenced. Therefore monitoring and detailed chemical and biological analysis is must before supplying the water for domestic purpose.