[en] It is stated that a strong water vapour maser has been observed at the position of a very compact radio and infra red source near the H II region NGC7538. The observation was made at night in May 1976 using the Efflesberg (Germany) 100 m telescope, fitted with a 384 channel autocorrelation spectrometer. The sudden appearance of the H₂0 source may be related to some unusual properties of the compact H II region. A schematic model for the source is shown. The exciting star is probably of spectral type 06, and is surrounded by one of the most compact H II regions known. This region is ionisation founded. There appears to be evidence for a high dust density within the H II region, since the silicate absorption is one of the strongest known. Formaldehyde is seen in emission from the source. The age of the source appears to be <= 10³ years. The source may be a useful prototype for the study of newly formed 0 stars and H₂0 masers. (U.K.)