Yes, damage from sewage can be dangerous. Sewage water is grossly contaminated water that poses serious risks to human health. Sewage can be contaminated with dangerous bacteria, parasites, and viruses. These pathogens and parasites can cause serious infections and diseases that can be life threatening. Because of this, it's important to always have sewage damage professionally mitigated. Improperly cleaned and dried sewage is a risk not worth taking.