I can't understand people who buy insurance unless it's absolutely necessary, while not as dramatic as a bombing we regularly get floods here in the UK and every time it happens the insurance companies have fucked off with peoples money and never paid it, get a secure savings account or put your money in Bitcoin and hide it away somewhere in case of an emergency.
Many floods do not happen enough to make it economical for people to be able to self insure as you describe. Many floods only happen once every several decades when enough people are involved and a long enough time period is used, however one could easily happen early after someone were to start to self insure themselves against this and they would essentially not have enough to cover the loss/repairs.