  The deuterium fractionation of water can serve as a tracer for the chemical
and physical evolution of water during star formation and can constrain the
origin of water in Solar System bodies. We determine the HDO/H$_2$O ratio in
the inner warm gas toward three low-mass Class 0 protostars selected to be in
isolated cores, i.e., not associated with any cloud complexes. Previous sources
for which the HDO/H$_2$O ratio have been established were all part of larger
star-forming complexes. Targeting these isolated protostars allows comparison
of the water chemistry in isolated and clustered regions to determine the
influence of local cloud environment. We present ALMA observations of the HDO
$3_{1,2}$-$2_{2,1}$ and $2_{1,1}$-$2_{1,2}$ transitions at 225.897 GHz and
241.562 GHz along with the H$_2^{18}$O $3_{1,3}$-$2_{2,0}$ transition at
203.407 GHz. The high angular resolution (0\farcs3-1\farcs3) allow the study of
the inner warm envelope gas. Model-independent estimates for the HDO/H$_2$O
ratios are obtained and compared with previous determinations in the warm gas
toward low-mass protostars. We detect the targeted water transitions toward the
three sources with S/N > 5. We determine the HDO/H$_2$O ratio toward L483, B335
and BHR71-IRS1 to be ($2.2\pm0.4$)$\times 10^{-3}$, ($1.7\pm0.3$)$\times
10^{-3}$, and ($1.8\pm0.4$)$\times 10^{-3}$, respectively, assuming
$T_\mathrm{ex} = 124$ K. The degree of water deuteration of these isolated
protostars are a factor of 2-4 higher relative to Class 0 protostars that are
members of known nearby clustered star-forming regions. The results indicate
that the water deuterium fractionation is influenced by the local cloud
environment. This effect can be explained by variations in either collapse
timescales or temperatures, which depends on local cloud dynamics and could
provide a new method to decipher the history of young stars.
