Is real water made up of heavy water and light water? I need to know, is real water made up of heavy water which is formed with deuterium, and light water which is water by protium?
We know that hydrogen has three major isotopes, including protium and deuterium.
We also know that water, $\ce{H2O}$, is made up by hydrogen and oxygen.
All this might mean that real water itself can naturally contain some heavy water - Deuterium oxide. Is this correct?
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”.)