**Ewa Krogulec, Jerzy J. Małecki, Dorota Porowska \* and Anna Wojdalska**

Faculty of Geology, University of Warsaw, Zwirki i Wigury 93, 02-089 Warsaw, Poland; ˙ ewa.krogulec@uw.edu.pl (E.K.); jerzy.malecki@uw.edu.pl (J.J.M.); a.b.wojdalska@uw.edu.pl (A.W.)

**\*** Correspondence: dorotap@uw.edu.pl

Received: 14 August 2020; Accepted: 3 November 2020; Published: 5 November 2020

**Abstract:** Monitoring the data of groundwater level in long-term measurement series has allowed for assessment of the impact of natural and anthropogenic factors on groundwater recharge. It allows for assessing the actual groundwater quantity, which constitutes the basis for balanced and sustainable groundwater planning and management in an urban area. Groundwater levels in three aquifers were studied: the shallow and deeper Quaternary aquifers and the Oligocene aquifer in Warsaw (Poland). Statistical analysis was performed on a 27-year (1993–2019) cycle of daily measurements of groundwater levels. The studies focused on determining the range and causes of groundwater level changes in urban-area aquifers. The groundwater table position in the Quaternary aquifer pointed to variable long-term recharge and allowed for the identification of homogenous intervals with identification of water table fluctuation trends. A decrease in the water table was observed within the Quaternary aquifers. The Oligocene aquifer displayed an opposite trend.

**Keywords:** potable supplies; groundwater level changes; infiltration; recharge; climate changes; water efficiency
