You can get swim ear on the plane but have a look online if you want to make sure youve got some. You can also get something called ear bandits. Its like an headband that covers the ears to stop water getting in. I shuld imagine its made from same stuff swim caps are.
As for ear infections I don't think its anything to do with the water not being ok. My son suffered in Egypt year before last and we have been to HV Turkey this year so i bought some ear plugs from boots for kids and some swim ear and he never had a problem.
When kids or any one are constantly in water they are going to be prone to the ear canal getting inflammed due to it constantly having water in it. You seem to notice this problem at large resorts as there are alot of people there.
There were 3000 people at HV Turkey so you are going to get a small percentage having problems or being ill, just like they would at home, but people seem to highlight it more on hol and straight away blame the hotel ( not saying that sometimes it will be hotels fault for illnesses, just before someone has a go at me, lololo

Jo