Hello chrisfromcorfu,
Welcome to Apple Support Communities. I understand form your post that your AirPods got washed in the washing machine and after drying the sound has an echo and you want to know if there is a way of preventing any kind of water damage. I am happy to provide some information.
Your AirPods and charging case aren't waterproof or water resistant, so be careful not to get moisture in any openings.
If your AirPods come in contact with liquid, including sweat from a workout, wipe them down with a dry microfiber cloth. To dry the case, place it upside down with the lid open.
If an AirPod becomes damaged after it gets wet, you can chat or talk with us to order a replacement."
How to clean your AirPods and EarPods
Let me know if you have any questions.
Have a great day!