What concern could an onsite sewage facility present to a water purveyor?

The correct choice highlights the potential risk of contamination that an onsite sewage facility might pose to a water supply, particularly if there is an improperly managed or direct connection to a landscape irrigation system. If there is cross-contamination between the onsite sewage facility and the irrigation system, treated wastewater from the facility could unintentionally mix with the potable water used for irrigation. This creates significant public health concerns due to the introduction of pathogens or contaminants that could reach the potable water supply.

In contrast, inadequate waste disposal mainly pertains to environmental risks but does not directly link to risks for water purveyors in the manner that water contamination does. While higher levels of water consumption and increased water treatment costs are valid concerns, they do not emphasize the direct impact that an onsite sewage facility can have on water quality and safety. Thus, the connection to irrigation systems specifically underscores a critical aspect of safeguarding public health and ensuring that the water supply remains uncontaminated.