Besides the dangers of antibiotic resistance, contaminated water can contain multitudes of viruses that don’t respond to oral antibiotics anyway. Some examples are Hepatitis A, Coxsackie A, norovirus...“stomach bugs” (gastroenteritis) and conjunctivitis can be either bacterial or viral. There can also be parasites such as giardia in contaminated water that don’t respond to antibiotics. The way these typically enter drinking water is through sewage contamination. It can happen anywhere, but more likely in some places and highly unlikely in others.