Different zirconium dioxide phases exhibit attractive functional properties, making them suitable for various applications. Among these, orthorhombic o-ZrO₂ is of particular interest due to its distinctive ferroelectric behavior. However, synthesizing phase-pure o-ZrO₂ thin films has remained challenging. Here, we demonstrate a robust water-based atomic layer deposition (ALD) process for o-ZrO₂ thin films using tris(dimethylamino)cyclopentadienyl zirconium as the precursor. The films were characterized by grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), ellipsometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and photoluminescence (PL) techniques. In the deposition temperature range of 225–250 °C, the process yielded nearly phase-pure o-ZrO₂ films with a growth-per-cycle (GPC) of 0.5 Å/cycle, whereas above 275 °C, monoclinic m-ZrO₂ films were obtained with GPC of 0.6 Å/cycle. Interestingly, longer relaxation times during deposition were found to affect the growth rate, which we tentatively attributed to changes in crystallization dynamics and stabilization of different orthorhombic space groups.