Which of the following features is characteristic of an antisiphon?

The characteristic feature of an antisiphon is its role in preventing backflow in irrigation systems. An antisiphon device is designed to ensure that water can only flow in one direction, thus preventing any contaminated water from returning to the clean water supply. This is crucial in irrigation to maintain the quality of the water used for agricultural purposes and to protect public health.

The functionality of an antisiphon is vital in systems where there is a risk of backpressure or potential negative pressure, where water might otherwise be siphoned back into the main water supply. By incorporating an antisiphon, irrigation systems can effectively safeguard against contamination, ensuring that only clean water is supplied to the irrigation lines.

This explains why the other options do not accurately describe the primary feature of an antisiphon. For example, while creating a vacuum effect might relate to variations in water pressure, it does not define the main purpose of an antisiphon. Enhancing soil absorption and increasing water pressure are not functions associated with an antisiphon, as the focus is on maintaining safe water flow rather than altering these other characteristics.