Have you tried a swimming cap? We used ear plugs & a swimming cap unless she was washing her hair.

I think its more about infection than anything. I read somewhere that splash water was ok, but dirty or soapy water needs to be avoided. I still avoided all water when possible.
They shouldn't go under water either. The pressure isn't good. DD got an earache just from swimming lessons & I think thats coz she was putting her head under.

You can use vasoline too. I often filled DD's ears with vasoline. After a while it just melts away. They can scratch it out, so you need to watch it, but its easy to put back in & not as easy to loose. I put the vaso in, then a bit of a cotton bud.