Ice , water , steam are all the same substance that is water as changing of water to any of its other two  forms solid or gas is a physical change.Only its physical state changes and there is no new substance formed . so they are all the same substance.  
1 1 1
Ice is gaseous water is liquid and steam is vapour are the three different states of a substance.they are not different substances because if you cool steam then you will get the liquid state the water and if you boil the liquid you will get the steam means the vapour/gas. and if you and if you heat the ice then you will get the liquid means the water.
                        by doing this you are getting the same thing therefore steam, water and ice are the different states of a substance and not a different substance in itself.
                   i hope that this will help u.       
1 1 1