The area of Cieszyn belongs entirely to the Odra drainage basin and Baltic Sea drainage area. The river system is well developed and the main watercourses within the town include:
• a section of the Olza river (9 km long, which is the western border of the town and simultaneously the Polish-Czech border) and its right-bank tributaries,
• the Puńcówka,
• the Bobrówka,
• the Piotrówka (a short source section in the northern part of the town).

The Bobrówka divides the town into the northern and eastern side and its right-bank tributaries (which drain the northern part of the town) include the Kraśnianka with the Bilowiec (Bielowiec), the Boguniówka, the Sarkandrowiec, and the Sarkander. In the southern part of Cieszyn the main watercourses include the Puńcówka, the Glinik (the upper part of the stream which joins the Puńcówka beyond the administrative boundaries of Cieszyn) and the Młynówka (an artificial watercourse coming from the Olza and joining the Bobrówka; at a short section in the area of Pod Wałką Park it joins the Puńcówka). Moreover, in the northern part of the town, the Kalembianka stream flows directly into the Olza. Apart from these streams and rivers there are other smallish and usually periodical water courses.
      Because flysch rocks show small water-retaining capacity and large share of water resistant shales (which do not favour infiltration), a large amount of meteoric water flow away on the surface or subsurface layer of the ground. Taking into account the small proportion of forested land in Cieszyn, (as in the whole area of Cieszyn Plateau) this causes sudden changes of water runoff and high water stages in streams and rivers. The largest mean discharges at the Olza occur in March and April and they are about 40% larger than the mean annual value. The second maximum occurs in July (120% of the mean annual discharge). The smallest discharges, at the level of 60-70% of the mean annual discharge, are recorded in October and November.
      Water reservoirs in Cieszyn represent entirely artificial reservoirs, mainly fishing ponds located in stream valleys. The largest group of ponds is located in the Kraśnianka valley (Cieszyn Gułdowy). A small boating lake is located at the Młynówki channel in Pod Walką Park. Flysch sediments of the Cieszyn nappe are generally poor in groundwater. In addition the water-bearing capacity of Quaternary sediment overlying flysch is either low or very low. In many places shallow groundwater horizons are observed connected with the weathering rock mantle.
      In the sediments infilling valley bottoms (these are sediments of medium water-bearing capacity) there is a groundwater aquifer of the free water-table, which in the Olza valley occurs at a depth of 2-4 m, and in the Bobrówka valley at a depth from several centimetres to 2 m and, on valley slopes, it joins the waters occurring in the rock mantle. The groundwater-table varies during the annual cycle. Deeper groundwater aquifers are not important in economic terms because of their significant mineralization or limited efficiency.