Natural disaster cleanup is an association community responsibility

This summer a record rainfall overwhelmed the city sewers and backed up into many homes throughout the city, including some lower units of our 3-story condo building. Those units paid the bill for clean up because the City refused, saying this was an "act of God." What kind of language could we propose to make it clear that similar disasters are a condo community responsibility, not just the individual whose unit(s)happen to get in the way? Is there some standard language about when disaster strikes it's a community responsibility? Thanks.