Wasserbehälter Hackenberg, Water reservoir in Döbling, Austria

The Hackenberg water reservoir is a double-chamber reservoir built in stamped concrete between 1908 and 1910, covered with earth and topped by a valve chamber. The visible valve chamber building, designed by Eduard Bodenseher senior, is made of partly bossed granite blocks in a Neo-Romanesque-Secessionist style. Behind a shallow rectangular basin with a stone balustrade on three sides, a three-arched arcade leads to the valve chamber entrance. The flat roof is laid out as a terrace with a four-sided belvedere and a pergola on stone pillars.

Built between 19 October 1908 and the end of October 1910 as part of Vienna's Second High Spring Water Pipeline, the reservoir sits at about 295 metres above sea level on the Hackenberg. The pipeline itself was inaugurated on 2 October 1910 at Vienna City Hall in the presence of Emperor Franz Joseph I. The illustrated title page of the Illustrierte Kronen-Zeitung of 3 December 1910 used the reservoir's silhouette as a backdrop for that event.

The valve chamber, the only visible part of the reservoir, was designed by Eduard Bodenseher senior of the Vienna City Building Department. Its granite facade with a three-arch arcade and a four-sided belvedere on the roof terrace gives the structure a representative character. The building is a protected monument.

The location sits on a hillside and is reachable on foot from central Döbling, though the approach involves some uphill walking. The best view of the building comes from outside since it is a protected structure.

The 1908–1910 building site was supplied by a two-track inclined lift running from Krottenbachstrasse up 61 metres at 0.5 metres per second, driven by a 10 hp locomobile. The same engine turned a 3 hp dynamo powering a pump that raised construction water to the hill. Inside the pit, field-rail wagons were moved by horses or, over short stretches, by muscle power.