These factors can include improper installation, household toxics in the system, excess household cleaners in the system, or overuse of garbage disposals. Household toxics can include oil-based paints, solvents, and cleaners which kill important bacteria in the system.
Large amounts of water rushing into the on-site wastewater system at once can be hard on it as well, causing the water to not be processed correctly. The US EPA estimates that the average water use in a typical home is 70 gallons per person, per day. This is an enormous amount of water, and not all of it is necessary.