Abstract: A self-contained apparatus detects the absence of water in a cut plant container and signals an audible alert. The alert sounds periodically until an attendant refills the water. The apparatus is a slender rigid structure that can easily fit inside a narrow vase of cut flowers. The top portion that remains above the normal water level holds the battery and electronic circuitry. The bottom portion, which rests against the container bottom, holds the water sensor. Various means of electronically distinguishing water from air are disclosed: thermal, vibrations, viscosity, density, acoustic, electromagnetic (including capacitance, microwaves, optical and beta rays), electrical contact, electrochemical, floats and pressure. The sensor has cavities in its structure to protect the sensor from handling, water damage and contamination. Some cavities are flooded having an opening above and below the normal container water level; the water inside a flooded cavity matches the water level in the container.