dirty water

 one way water becomes contaminated is poop! because people poop in a hole so then the poop go's into the water so when you take a shower the water is contaminated and dirty and like you got poop in your body you take diaharrea and lose a lot of water and then u died                                      

the danger of having water contaminated is you can died because you lose a lot of water inside of you and you can also have worms inside of you and eat nutrient and your body dosen't absorb it  you can died 

a filter because the filter takes all the bad water and change it to clean water this happen because the filter takes all the bad stuff out of the water and safe for us to drink 

i don't think the  3 world dosen't have this invention because i don't think other people care