Yes, you can shower with lash extensions on. Try not to let water from the shower fall directly on your face as the pressure will make the lash extension loosen and shed faster.
How about swimming in a pool, lake, or ocean after getting lash extensions? If you just had your service done that day, most technicians recommend letting them set for four to eight hours. If you're doing laps in the pool or splashing in waves, you might want to consider wearing goggles to minimize the disturbance to your lash extensions.
Your lash technician should give you a spoolie brush for maintenance of lashes after your appointment. Use this post-shower or post-swim to gently brush through your extensions. This will help reshape lashes that are beginning to cling together or are pointing in different directions.