dengue fever causes flu-like  symptoms and can be lethal in extreme cases. application of insect repellent prior to entering a favela can help protect against infection. 

other risks associated with stagnant water are the contraction of illnesses such as hepatitis and bacterial-related diarrhea - reason why closed-toe shoes are important and stepping in water puddles should be avoided.

the random and often undetectable presence of poorly built or illegal electrical systems can result in water puddles being electrically charged with running power currents - thus, stepping in stagnant water and puddles can be both unhealthy and extremely dangerous.