You can download an app for your smart phone to keep track of when to expect your period. There are a ton of them available in the app store,just pick one and start using it. you'll have to enter the first day of each period and the last day in order for it to be able to calculate when your next one should be coming.
For the most part, water will stop you period so you don't need to work about it suddenly appearing in the pool, that won't happen. And as for wearing shorts you can do that too! It's unlikely you period would bleed through your shorts before you notice it has arrived. Just always keep a pad or tampon with you and you'll be fine!