Water is a polar molecule. This means that parts of the molecule are liklely to carry a charge. These are not sufficently strong for ionic attractions to be present between molecules however, the bonds are relativly strong, significant enough to allow such a small molecule to be a liquid at room temperature when many other similar small, covalently bonded molecules such as Carbon Dioxide are gases. This behaviour results becuse the oxygen end of the molecule has a slight negative charge and the hydrogen ends a slight positive. The net result is the hydrogens 'stick' to the oxygens and the oxygens to the hydrogens.
How does this affect the liquid?
it is immiscible with oils which are non polar.
This is demonstrated by a fun experiment involving oil, water food coloring and a bottle that has a lid (quite an important feature). IF you want to do this activity yourself, download the PDF activity card below.
Or alternatively you can watch the video that we filmed of our experiment in which the yellow oil layer seriates itself from the water containing black food coloring. This is (potentially) less messy and faster (15 minutes of footage in less than one) and should allow you to appreciate how this occurs. Just click play on the flash video you see below!
The polar water molecules have a tendency to be attracted to other polar water molecules rather than the non polar fats which results in them separating into two distinct layers.