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We present an analysis of the properties of neutral hydrogen (HI) in 248nearby (0.02<z<0.25) radio galaxies with $S_{\rm 1.4\, GHz}>30$ mJy and forwhich optical spectroscopy is available. The observations were carried out withthe Westerbork Synthesis Radio Telescope as the last large project before theupgrade of the telescope with phased array feed receivers (Apertif). The samplecovers almost four orders of magnitude in radio power from $\log\,P_{\rm 1.4\,GHz}=22.5$ W Hz$^{-1}$ and $26.2$ W Hz$^{-1}$. We detect HI in absorption in$27\% \pm 5.5\%$ of the objects. The distribution and kinematics of theabsorbing HI gas appear to depend on radio power, the properties of the radiocontinuum emission, and the dust content of the sources. Among the sourceswhere HI is detected, gas with kinematics deviating from regular rotation ismore likely found as the radio power increases. In these cases, the HI profileis often asymmetric with a significant blue-shifted component. This isparticularly common for sources with $\log\,P_{\rm 1.4 \, GHz}>24$ W Hz$^{-1}$,where the radio emission is small, possibly because these radio sources areyoung. The same is found for sources that are bright in the mid-infrared, i.e.sources rich in heated dust. In these sources, the HI is outflowing likelyunder the effect of the interaction with the radio emission. Conversely, indust-poor galaxies, and in sources with extended radio emission, at all radiopowers we only detect HI distributed in a rotating disk. Stacking experimentsshow that in sources for which we do not detect HI in absorption directly, theHI has a column density that is lower than $3.5\times 10^{17} (T_{ \rmspin}/c_f)$ cm$^{-2}$. We use our results to predict the number and type of HIabsorption lines that will be detected by the upcoming surveys of the SquareKilometre Array precursors and pathfinders (Apertif, MeerKAT, and ASKAP).

Kinematics and physical conditions of HI in nearby radio sources. The last survey of the old Westerbork Synthesis Radio Telescope