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MIRI/MRS on board the JWST allows us to probe the inner regions ofprotoplanetary disks. Here we examine the disk around the classical T Tauristar Sz 98, which has an unusually large dust disk in the millimetre with acompact core. We focus on the H$_2$O emission through both its ro-vibrationaland pure rotational emission. Furthermore, we compare our chemical findingswith those obtained for the outer disk from Atacama LargeMillimeter/submillimeter Array (ALMA) observations. In order to model themolecular features in the spectrum, the continuum was subtracted and LTE slabmodels were fitted. The spectrum was divided into different wavelength regionscorresponding to H$_2$O lines of different excitation conditions, and the slabmodel fits were performed individually per region. We confidently detect CO,H$_2$O, OH, CO$_2$, and HCN in the emitting layers. The isotopologueH$^{18}_2$O is not detected. Additionally, no other organics, includingC$_2$H$_2$, are detected. This indicates that the C/O ratio could besubstantially below unity, in contrast with the outer disk. The H$_2$O emissiontraces a large radial disk surface region, as evidenced by the graduallychanging excitation temperatures and emitting radii. The OH and CO$_2$ emissionare relatively weak. It is likely that H$_2$O is not significantlyphotodissociated; either due to self-shielding against the stellar irradiation,or UV-shielding from small dust particles. The relative emitting strength ofthe different identified molecular features point towards UV-shielding ofH$_2$O in the inner disk of Sz 98, with a thin layer of OH on top. The majorityof the organic molecules are either hidden below the dust continuum, or notpresent. In general, the inferred composition points to a sub-solar C/O ratio(<0.5) in the inner disk, in contrast with the larger than unity C/O ratio inthe gas in the outer disk found with ALMA.

MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI