  Although liquid water has been studied for many decades by (X-ray and
neutron) diffraction measurements, new experimental results keep appearing,
virtually every year. The reason for this is that neither X-ray, nor neutron
diffraction data are trivial to correct and interpret for this essential
substance. Since X-rays are somewhat insensitive to hydrogen, neutron
diffraction with (most frequently, H/D) isotopic substitution is vital for
investigating the most important feature in water: hydrogen bonding. Here, the
two very recent sets of neutron diffraction data are considered, both
exploiting the contrast between light and heavy hydrogen, $^1$H and $^2$H, in
different ways. Reverse Monte Carlo structural modeling is applied for
constructing large structural models that are as consistent as possible with
all experimental information, both in real and reciprocal space. The method has
also proven to be useful for revealing where possible small inconsistencies
appear during primary data processing: for one neutron data set, it is the
molecular geometry that may not be maintained within reasonable limits, whereas
for the other set, it is one of the (composite) radial distribution functions
that cannot be modeled at the same (high) level as the other three functions.
Nevertheless, details of the local structure around the hydrogen bonds appear
very much the same for both data sets: the most probable hydrogen bond angle is
straight, and the nearest oxygen neighbours of a central oxygen atom occupy
approximately tetrahedral positions.
