  Water is essential for life and technological applications, mainly for its
unique thermodynamic and dynamic properties, often anomalous or
counterintuitive. These anomalies result from the hydrogen-bonds fluctuations,
as evidenced by studies for supercooled water. However, it is difficult to
characterize these fluctuations under ambient conditions. Here, we fill this
knowledge gap thanks to the Car-Parrinello ab initio molecular dynamics (MD)
simulation technique. We calculate the local structural order parameter
{\zeta}, quantifying the coordination shells separation, and find two
locally-favored structures or states: High-{\zeta} and Low-{\zeta}. On average,
High-{\zeta} molecules have a tetrahedral arrangement, with four hydrogen
bonds, and the first and the second coordination shell well separated. The
Low-{\zeta} molecules are less connected, partially merging the first and the
second shells. The appearance of isosbestic points in the radial distribution
functions and the collective density fluctuations at different length scales
and timescales reveal that the two-state model, consistent with available
experimental data for supercooled water, also holds under ambient conditions,
as we confirm by analyzing the vibrational spectrum of both types of water
molecules. Significant consequences of the structural differences between the
two states are that High-{\zeta} molecules have a dipole moment 6 % higher than
Low-{\zeta}. At the same time, Low-{\zeta} structures are more disordered and
with more significant angular fluctuations. These differences are also
reflected in the dynamics under ambient conditions. The Low-{\zeta} molecules
decorrelate their reorientation faster than High-{\zeta} and merge their
coordination shells within 0.2 ps, while the High-{\zeta} preserve the shell
separation for longer times.
