However, water coming clean from the sources hundreds of kilometers away may be polluted due to rusty internal plumbing equipments of buildings and neglected water storage tanks. Every tank that does not receive proper cleaning is a source of microbes. Furthermore old plumbing equipments and tanks do not only spoil the water quality in time but also start to host heavy metals that cause permanent damage to human health.  Therefore the rusty equipments should be renovated and the network water should be used directly from the network, instead of supply from water storage tanks.
Tap water in İstanbul is analyzed in scientific platforms upon collection of samples from 150-200 points every day. The outlet water from treatment plants and all the processes this water proceeds through the network to our taps is controlled on a regular basis. The potable water is given to the urban network upon testing various parameters. These parameters include bacteriological, physical and chemical ones.
İSKİ inspects whether the standards of potable water are met, conducts necessary analyses and announces these results on a monthly quality report. The outlet water from plants and network water reaching to customers are checked for their compliance with the TSE-266 Standards for Potable and Use Water in bacteriological and chemical ways. Furthermore, water reservoirs, wells, springs and foundation waters are also monitored for quality.
İSKİ maintains water quality control duties in four stages: 
1- Sampling and control
2- Chemical and bacteriological laboratory studies
3- Warning-coordination
4- Disinfection and discharge

1- Sampling and control:

İSKİ samples from 350-400 potable water points within its service area a day. The samples are collected every morning from a pre-identified program screening the network. These samples undergo a chemical analysis at Kağıthane Central Laboratory. Certain samples are monitored at the sampling site.

2- Chemical and bacteriological laboratory studies:
The Chemical Laboratory seeks the compliance of water to TSE-266 Standards for Potable and Use Water parameters. Various analyses are conducted to make sure the potable water bears no unhealthy conditions in chemical terms. From physical look of the water to its rigidity, from anions and cations to materials causing odour and taste, from pesticides to disinfection by-products, various parameters are measured.
In the Bacteriology Laboratory, 350-400 daily samples from treatment plants, network lines, industrial subscribers, wells, lakes and dams under İSKİ’s responsibility are analyzed in bacteriological ways. Furthermore, more samples are taken and analyzed upon complaints from subscribers.

3- Warning-coordination: 
In order to prevent the pollution identified upon the evaluation of samples from the network, İSKİ provides coordination with all related departments. In locations with pollution, instant addressing is possible thanks to the computer network.