You can see in this particular structure, there is a hydrogen bond between a hydrogen on the hydronium ion and the oxygen on the other water molecule.
Hydronium ions don’t exist in on their own, they’re required to have some way of balancing the charge that comes from the additional hydrogen ion. This balancing is typically done by the water surrounding the hydronium ion (H3O+H3O+) since water will outnumber the amount of hydronium atoms by orders of magnitude (there’s a lot more water than ions).
The hydronium ion in cold water is typically surrounded by 6 water molecules (probably oxygen towards the extra hydrogen but I can’t access the journal to confirm). There are some other structures like the one above, and another called the Eigen cation where the hydrogen is at the center of four water molecules (one is technically the hydronium). There’s also a very large structure that’s called the magic structure that has a hydronium ion surrounded by twenty water molecules (it’s called magic because it’s extra stable for its size).
