Welcome back from your trip Ken. Good pictures of a household cistern but not limited to Cuba, these are used in most houses in Central and South America as well as some areas of the US. I lived with similar in about five different homes over 10 years in Mexico but ours were almost always on the roof and also supplied sufficient pressure for the house water system and would hold enough for about a weeks use in case of power outage etc.
Cheers, Flygt