"We had a basement flood after a storm, do we have to disclose it to a buyer?"
Simple answer - no.
A one-off event is no different than say a tree falling on your roof or a stove fire, etc.
Only when there is a strong chance of a recurrence does something have to be disclosed.
I will not get deep into blatant vs. latent defects, but blatant simply means, "easily found" while latent mean, "concealed." I have overly simplified.
So, what about homes with recurring water issues? The worst I have seen, how about every day! The city screwed up, the sewer system is at fault, they eventually built a large catch basin, very large outside of the house and everyday, after a rain, a city truck comes to pump out the water. Do you think that a potential buyer should know of this?
In another case, a high-end luxury residence, backing onto a golf course, new owners moved in, flood happened right after a storm. The basement was ruined. They called the insurance firm and the insurance firm called them back. They had checked records and the previous owner had 3 previous claims for flooding. The new owners are currently suing the sellers and the Realtor who acted for both parties.
I have had situations, mostly pertaining to bad city engineering of up to 10 sewer back ups. One, in Etobicoke, Toronto was so bad that I actually gave a ZERO market value as even if the house were to be demolished the lot would still flood due to the sewers and drainage.
So, a one-off, no. Recurring, not only is it good practice it is the ethical thing to do.