Water supply buildings Žlutý kopec, Water tank complex in Old Brno, Czech Republic.

The Water supply buildings at Žlutý kopec consist of three underground reservoirs built into the hillside between Tvrdého and Tomešova streets. The first reservoir is a single brick tank measuring 45 by 45 metres and 6 metres deep, lined with clay for waterproofing. The second, from 1896–1900, is a similar brick tank of 45 by 70 metres. The third, from the 1910s, comprises two concrete tanks of about 30 by 35 and 30 by 45 metres, over 5 metres deep. A former technical house stands between the first two reservoirs.

Brno approved a new water supply project in 1869, designed by English builder Thomas Docwry. The first reservoir on Žlutý kopec was built in 1869–1872, a brick tank 45 × 45 m and 6 m deep, fed by the Pisárky treatment plant drawing from the Svratka. A second brick tank (45 × 70 m) followed in 1896–1900, and a third reservoir with two concrete tanks in the 1910s. The reservoirs were taken out of service on 18 March 1997 because of their low position, and in 2019 they were declared a cultural monument.

The site is managed by TIC Brno, the city's tourist information office, which opened the reservoirs for guided visits. The first brick reservoir was made accessible in July 2020, the two brick tanks reopened in October 2022, and the whole complex including the concrete reservoir opened on 22 March 2024. The reservoirs were declared a cultural monument in 2019.

This underground complex requires sturdy footwear and careful footing due to its subterranean layout. Having a guide helps you navigate the narrow passages between pillars and understand how the water storage system functions.

The brick reservoirs are lined with clay for waterproofing, and the first tank measures 45 by 45 metres at a depth of 6 metres. The second, built 1896–1900, is 45 by 70 metres. The third reservoir, from the 1910s, consists of two concrete tanks of roughly 30 by 35 and 30 by 45 metres.