@pilonpl it might also depend on how acidic or alkaline the water is. if you have pH of like 3 you will have a lot of H3O+/H+ ions. When you have a pH of 10 you will have a lot of OH- ions.
However i dont think this changes the total number of hydrogen atoms as long as no reaction happens since neutral water at pH7 has H2O + H2O <—> H3O+ + OH- still has the same amount of hydrogen.
Hmmm but u still need to make the water go from neutral to acidic or alkaline so theres chance. When you add amonia NH3 to water it will become alkaline. NH3 + H2O <—> NH4+ + OH- leaving you with an odd number of hydrogen atoms (as long as the reaction doesnt happen as multitudes of 2). there will also be an unkown number of either odd or not odd ammonia NH3 molecules that dont react that will further change the hydrogen count
So as long as the water isnt contaminated or you dont let it react with something there should always be multiple of 2 hydrogen atoms in the water since 1 hydrogen alone shouldnt exist. But if u had hydrochloric acid HCl or any other chemical containing odd numbers of H in the water there might be an odd number of hydrogen in the water overall.
At least thats how far my knowledge goes, maybe i missed something. (edited)
