This week Nel's looking at the interesting but sometimes disgusting world of waste.
Back in the Victorian times, raw sewage went straight into the streets, the sea, and rivers. Not only did that create a huge stink but disease spread easily.
The answer was to put in a new underground sewer system but now there are so many of us using it, the system is struggling to cope.
Billions of litres of sewage is treated around the UK every day but not all of it is going to waste.