What is the concentration of hydronium and hydroxide ions in pure water?

The pH of distilled (pure) water is equal to 7.

The concentration of OH - (hydroxide) and H3O + (hydronium) is equal to 14:

[H3O+]+[OH-]=10^-14

Since we know pH is the - log of hydronium concentration, we can use our value of 7 pH and do. the opposite log (10^-7) so therefore the concentrations of both will be equal to 10^-7