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Transmission spectroscopy of exoplanets has the potential to provide precisemeasurements of atmospheric chemical abundances, in particular of hot Jupiterswhose large sizes and high temperatures make them conducive to suchobservations. To date, several transmission spectra of hot Jupiters haverevealed low amplitude features of water vapour compared to expectations fromcloud-free atmospheres of solar metallicity. The low spectral amplitudes insuch atmospheres could either be due to the presence of aerosols that obscurepart of the atmosphere or due to inherently low abundances of H$_2$O in theatmospheres. A recent survey of transmission spectra of ten hot Jupiters usedempirical metrics to suggest atmospheres with a range of cloud/haze propertiesbut with no evidence for H$_2$O depletion. Here, we conduct a detailed andhomogeneous atmospheric retrieval analysis of the entire sample and report theH$_2$O abundances, cloud properties, terminator temperature profiles, anddetection significances of the chemical species. Our present study finds thatthe majority of hot Jupiters have atmospheres consistent with sub-solar H$_2$Oabundances at their day-night terminators. The best constrained abundancesrange from $\mathrm{log(H_2O)}$ of $-5.04^{+0.46}_{-0.30}$ to$-3.16^{+0.66}_{-0.69}$, which compared to expectations from solar-abundanceequilibrium chemistry correspond to $0.018^{+0.035}_{-0.009}\times$ solar to$1.40^{+4.97}_{-1.11}\times$ solar. Besides H$_2$O we report statisticalconstraints on other chemical species and cloud/haze properties, includingcloud/haze coverage fractions which range from $0.18^{+0.26}_{-0.12}$ to$0.76^{+0.13}_{-0.15}$. The retrieved H$_2$O abundances suggest sub-solaroxygen and/or super-solar C/O ratios, and can provide important constraints onthe formation and migration pathways of hot giant exoplanets.

H$_2$O abundances and cloud properties in ten hot giant exoplanets