If you are serious about your training, you may want to invest in an activity tracker. The model is waterproof.
From OnBuy
Polar Unisex A370 Activity Tracker with Continuous Heart Rate, Black, Medium/Large
The Watch Hut
Unisex Polar A370 Bluetooth GPS HR Activity Tracker Alarm Chronograph Watch 90064877 - LCD / White
Watch Shop
Polar A370 Fitness Tracker - LCD / White
The Fitness Store
Polar Polar A370