Question: How long after the Chernobyl disaster was the Kiev water supply adjusted?
About the article "Chernobyl disaster", section "Rivers, lakes and reservoirs".

Candidate passages:
Chernobyl or Chornobyl (IPA ; , ; , , Polish "Czarnobyl") is a city in the restricted Chernobyl Exclusion Zone situated in northern Kiev Oblast, Ukraine near the border with Belarus.
The city had been the administrative centre of the Chernobyl Raion since 1932.
The city was evacuated in 1986 owing to the Chernobyl disaster at the Chernobyl Nuclear Power Plant, located north-northwest.
The power plant was within Chernobyl Raion (District), but the city was not the residence of the power plant workers.
When the power plant was under construction, Pripyat, a city larger and closer to the power plant, had been built as home for the power plant workers.
After the accident the Chernobyl Raion administration was transferred to the neighboring Ivankiv Raion.
Though the city today is mostly uninhabited, a small number of people reside in houses marked with signs stating that the "Owner of this house lives here".
Workers on watch and administrative personnel of the Zone of Alienation are stationed in the city on a long term basis.
Prior to its evacuation, the city was inhabited by about 14,000 residents.
The city of Slavutych was built specifically for the evacuated population of Chernobyl. 
Daniel Milstein was born in Kiev, Ukraine.
He and his family relocated to the United States after the Chernobyl nuclear disaster.
He received his education with honors in business management and finance and graduated with a BBA from Cleary University, Ann Arbor. 
Slavutych () is a city in northern Ukraine, purposely-built for the evacuated personnel of the Chernobyl Nuclear Power Plant after the 1986 disaster that occurred in the city of Chernobyl.
Geographically located within the Ripky Raion, Chernihiv Oblast, Slavutych is administratively subordinated to the Kiev Oblast as a "city of regional significance".
As of 2007, the city population was 24,549. 
  Chernobyl disaster  Chernobyl disaster effects  Chernobyl compared to other radioactivity releases  Cultural impact of the Chernobyl disaster  Deaths due to the Chernobyl disaster  Individual involvement in the Chernobyl disaster  Chernobyl necklace  Radiophobia  
Residual radioactivity in the environment.
Rivers, lakes and reservoirs.
The Chernobyl nuclear power plant is located next to the Pripyat River, which feeds into the Dnieper reservoir system, one of the largest surface water systems in Europe, which at the time supplied water to Kiev's 2.4 million residents, and was still in spring flood when the accident occurred.
The radioactive contamination of aquatic systems therefore became a major problem in the immediate aftermath of the accident.
In the most affected areas of Ukraine, levels of radioactivity (particularly from radionuclides 131I, 137Cs and 90Sr) in drinking water caused concern during the weeks and months after the accident, though officially it was stated that all contaminants had settled to the bottom "in an insoluble phase" and would not dissolve for 800–1,000 years.
Guidelines for levels of radioiodine in drinking water were temporarily raised to 3,700 Bq/L, allowing most water to be reported as safe, and a year after the accident it was announced that even the water of the Chernobyl plant's cooling pond was within acceptable norms.
Despite this, two months after the disaster the Kiev water supply was abruptly switched from the Dnieper to the Desna River.
Meanwhile, massive silt traps were constructed, along with an enormous 30m-deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River.
Bio-accumulation of radioactivity in fish resulted in concentrations (both in western Europe and in the former Soviet Union) that in many cases were significantly above guideline maximum levels for consumption.
Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1,000 Bq/kg in the European Union.
In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the years after the accident.
In small "closed" lakes in Belarus and the Bryansk region of Russia, concentrations in a number of fish species varied from 100 to 60,000 Bq/kg during the period 1990–92.
The contamination of fish caused short-term concern in parts of the UK and Germany and in the long term (years rather than months) in the affected areas of Ukraine, Belarus, and Russia as well as in parts of Scandinavia.