Use this [guide|40007|teardown] to start your water damage repair. It's not a definite tear down, but it brings you to taking out the motherboard at least.
Then use the [[Electronics Water Damage|Water Damage Guide]] for how to clean up the phone. Be very careful. The guide really is important because you don't want further corrosion in your phone.
If it doesn't power up still, I would look into another battery. As long as the phone doesn't have a password or code and the device still turns on, you should be able to connect it to a PC to get your customer's pictures.
Please keep us updated and good luck!
[https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Dmobile&field-keywords=moto+E+replacement&tag=ifixitam-20|Replacement Parts]