The aquatic warbler breeds in the western Palearctic, and its winter ranges are located in western Africa, in the south of the Sahara. During the migration it appears in countries of western Europe such as Germany, Holland, Belgium, France, United Kingdom and Spain.

During the nesting period, it is distributed in the western Paleartic, from Germany to the Urals in Russia. Nowadays there are breeding populations in Germany, Poland, Latvia, Lithuania, Russia, Belorussia, Ukraine and Hungary. During the last century this distribution area has decreased. The aquatic warbler has disappeared from France, Belgium, Holland, western Germany, Austria, Italy and the ex-republics of Czechoslovakia and Yugoslavia.

The most recent calculation of its population, by the "Team of Study of the Aquatic warbler", estimates between 12.484 and 19.915 the number of males defending their territory in the breeding areas.