What happens when water enters a tracheostomy?

Coughing. It is the same as if water just "goes down the wrong way." the patient will cough and clear the water.
Aspiration. A trachesotomy is an opening (ostomy) in the front of the neck that connects your windpipe (trachea) to the outside world directly. They can be temporary or permanent. If water enters a tracheostomy, coughing due to bronchospasm will occur as a protective mechanism can occur. Significant amount can lead to an aspiration pneumonia. If enough water enters, it can lead to drowning and death.
Could drown. A little water can be coughed out or suctioned. A lot could kill.