Is real water made up of heavy water and light water?
Water has formula H2O. Oxygen has 3 stable isotopes (99.76% 16O, 0.039% 17O, 0.201% 18O), and hydrogen has two (99.985% 1H, 0.015% 2H). Thus, there are 9 natural isotopic configurations for water: 3 possibilities for oxygen, multiplied by 3 possibilities for 2 hydrogens with 2 possible isotopes.

Out of those 9 possible configurations, only 4 have a natural abundance larger than 1 ppm:

                        

So, pure water is a mixture of 9 different isotopic configurations. You will note that D2O, which is what is usually called heavy water, is not actually among the 4 more common isotopic configurations given by natural abundance.



Also of note: water that is not “heavy water” is sometimes called “light water”, but never “soft water”. “Soft water” is a term used for a chemical process of natural (non pure) water that has been depleted from certain metal cations. (It is used in contrast to “hard water”.)