The Landlord would likely argue that an emergency/exigent circumstance (i.e. potential water damage) allowed and justified Landlord to enter the Tenant's unit. Without the existence of the water leak or some other reason justifying their entrance, the Landlord could be guilty of a forcible entry and certain statutory damages.
Please be advised we do not have an attorney/client relationship and this is not legal advice. You should hire an attorney to provide you with legal assistance.
If this is the first time it happened, ignore it. If it happens again, you need to discuss boundaries with your landlord. You can always put a chain on the door and keep it locked when you are home.
Disclaimer: The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.
This is a genuine emergency, so yes, the landlord can neter without waiting for permission.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.