Water in ear. If you are getting an external ear canal infections (otitis externa, also known as swimmer's ear), it is because water is getting trapped in your ear canal, making a good place for bacteria and fungus to grow. Excess ear wax can predispose to water trapping, as can allowing the water to flow directly into your ear. You can ask your doctor if you have a lot of wax and re-direct the water flow.
Ear infections. It is possible that you get water in your outer ear canals causing a "swimmer's ear" like condition. Try using 3-5 drops of ordinary white vinegar in both ears after your should to prevent infection.