  We consider one-dimensional interacting quantum fluids, such as the
Lieb-Liniger gas. By computing the low-temperature limit of its (generalised)
hydrodynamics we show how in this limit the gas is well described by a
conventional viscous (Navier-Stokes) hydrodynamics for density, fluid velocity
and the local temperature, and the other generalised temperatures in the case
of integrable gases. The dynamic viscosity is proportional to temperature and
can be expressed in a universal form only in terms of the emergent Luttinger
Liquid parameter $K$ and its density. We show that the heating factor is finite
even in the zero temperature limit, which implies that viscous contribution
remains relevant also at zero temperatures. Moreover, we find that in the
semi-classical limit of small couplings, kinematic viscosity diverges,
reconciling with previous observations of Kardar-Parisi-Zhang fluctuations in
mean-field quantum fluids.
