  Transmission spectroscopy of exoplanets has the potential to provide precise
measurements of atmospheric chemical abundances, in particular of hot Jupiters
whose large sizes and high temperatures make them conducive to such
observations. To date, several transmission spectra of hot Jupiters have
revealed low amplitude features of water vapour compared to expectations from
cloud-free atmospheres of solar metallicity. The low spectral amplitudes in
such atmospheres could either be due to the presence of aerosols that obscure
part of the atmosphere or due to inherently low abundances of H$_2$O in the
atmospheres. A recent survey of transmission spectra of ten hot Jupiters used
empirical metrics to suggest atmospheres with a range of cloud/haze properties
but with no evidence for H$_2$O depletion. Here, we conduct a detailed and
homogeneous atmospheric retrieval analysis of the entire sample and report the
H$_2$O abundances, cloud properties, terminator temperature profiles, and
detection significances of the chemical species. Our present study finds that
the majority of hot Jupiters have atmospheres consistent with sub-solar H$_2$O
abundances at their day-night terminators. The best constrained abundances
range 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-abundance
equilibrium 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 statistical
constraints on other chemical species and cloud/haze properties, including
cloud/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-solar
oxygen and/or super-solar C/O ratios, and can provide important constraints on
the formation and migration pathways of hot giant exoplanets.
