I read some very interesting statistics on Cuba's sewage treatment like this:
"Despite its clear importance to the citizens of Cuba, the treatment of urban sewage in particular is extremely limited: only 17 or 18 percent receives any treatment before discharge into Cuban waterways. (3) The infrastructure of water and sanitation are beyond the breaking point and are close to catastrophic failure. Havana’s sewer system, which was built almost a hundred years ago, has been due for major repairs for almost five decades and is serving over two million citizens, well beyond its design capacity of 400,000. (4)"
Go here for the entire eye-opening report.