Does pure water contain any H3O+ ions? Explain your answer.
pure water contain ions and the process is called autoionization (or self-ionization) of water.
That happens because water can act both as an acid, donating a proton, H+, to another water molecule, which acts as a base.
The reaction results in the formation of the hydronium ion, or H3O+, and of the hydroxide ion, HO−.
However, the concentration of hydronium and hydroxide ions will be very, very small; in fact, the equilibrium that's established in solution lies so far to the left, that only 18 in 1010 molecules of water will undergo autoionization.