The final results for Narva river water runoff estimation have shown that long–term discharge of Narva river in Narva city calculated by Estonian and Russian specialists could differ up to 30%. This difference is caused by use of different methods for estimating water discharge. This, in turn, means that estimated pollution load from both countries can also vary up to 30%.
The simultaneously measured Narva river water discharges during the Narva WATMAN project implementation were very similar, the difference was less than 5%. This deviation is acceptable in accordance with the rules of the World Meteorological Organization, of which both countries are members.
Methods for chemical analysis of water did not vary to a large extent in two countries. However, some laboratory tests and procedures differ in Estonia and Russia. Water quality assessment indicators were also different. All these differences must be taken into account when developing a harmonized runoff calculation and water quality indicators methodologies.