Context : Shock-induced H _ { 2 } O masers are important magnetic field tracers at very high density gas .
Water masers are found in both high- and low-mass star-forming regions , acting as a powerful tool to compare magnetic field morphologies in both mass regimes .

Aims : In this paper , we show one of the first magnetic field determinations in the low-mass protostellar core IRAS 16293-2422 at volume densities as high as 10 ^ { 8 - 10 } cm ^ { -3 } .
Our goal is to discern if the collapsing regime of this source is controlled by magnetic fields or other factors like turbulence .

Methods : We used the Very Large Array ( VLA ) to carry out spectro-polarimetric observations in the 22 GHz Zeeman emission of H _ { 2 } O masers .
From the Stokes V line profile , we can estimate the magnetic field strength in the dense regions around the protostar .

Results : A blend of at least three maser features can be inferred from our relatively high spatial resolution data set ( \sim 0.1 ^ { \prime \prime } ) , which is reproduced in a clear non-Gaussian line profile .
The emission is very stable in polarization fraction and position angle across the channels .
The maser spots are aligned with some components of the complex outflow configuration of IRAS 16293-2422 , and they are excited in zones of compressed gas produced by shocks .
The post-shock particle density is in the range of 1 - 3 \times 10 ^ { 9 } cm ^ { -3 } , consistent with typical water masers pumping densities .
Zeeman emission is produced by a very strong line-of-sight magnetic field ( B \sim 113 mG )

Conclusions : The magnetic field pressure derived from our data is comparable to the ram pressure of the outflow dynamics .
This indicates that the magnetic field is energetically important in the dynamical evolution of IRAS 16293-2422 .