  Here I show that experimental and simulation data on liquid water using
vibrational (infrared and Raman) and X-ray (absorption and emission)
spectroscopies, as well as recent data from X-ray scattering, are fully
consistent with a two-state picture of water. At ambient conditions there are
fluctuations between a dominating high-density liquid (HDL) and a low-density
form (LDL). These are related to the two forms of amorphous ice at very low
temperature, high-density amorphous (HDA) and low-density amorphous (LDA),
which interconvert in a first-order-like transition. This transition line is
assumed to continue into the so-called No-mans land as a liquid-liquid
transition and terminate in a critical point with very large fluctuations
between the two liquid forms. These fluctuations extend in a funnel-like region
up to ambient temperatures and pressures and give water its unusual properties
which are fundamental to life. With this picture we find simple, intuitive
explanations of the anomalous properties of water, such as the density maximum
at 4 C, why ice floats, and why the compressibility and heat capacity grow as
the liquid is cooled. We summarize by noting that in this picture, water is not
a complicated liquid, but two normal liquids with a complicated relationship.
