Household wastewater contains some contaminants that degrade water quality for such uses as drinking, stock watering, food preparation and cleaning. Potential contaminants in household wastewater include disease-causing bacteria, infectious viruses, household chemicals, and nutrients, such as nitrate. Viruses can infect the liver, causing hepatitis or infect the lining of the intestine, causing gastroenteritis (vomiting and diarrhea). If coliform organisms (a group of indicator bacteria) are found in well water, they show that the water is potentially dangerous for drinking and food preparation. Virtually all farmsteads use a septic system or similar on-site wastewater treatment system.