This is a very difficult question to answer as every patient is an individual.
I always say to patients not to get water in the ears until I see them at the first Out-Patients appointment. At that stage I reiterate that they have an artifically created hole in the eardrum by virtue of the fact the grommet is in place. I then suggest should they wish to swim they should use good ear seals to prevent water entering the ear canal. If children, I also suggest the headbands that can be worn to further prevent water from entering the ear canals.
Clearly if patients develop infections despite ear precautions as above I explain it is more appropriate to avoid putting the ears at risk with certain activities such as swimming.