A water bath is a laboratory device used to incubate samples in water at a controlled, constant temperature over extended periods. It consists of a heated tank filled with water, typically made of stainless steel or corrosion-resistant material, with insulated walls to reduce heat loss and often a lid to prevent evaporation. Temperature is regulated by a thermostat, with digital or analog controls achieving accuracy commonly within ±0.1°C to ±1°C, and immersion heaters distribute heat evenly throughout the bath.
Water baths are available in several variants. Shaking water baths gently agitate samples, making them suitable for cell culture and enzymatic reactions. Circulating water baths use pumps to maintain uniform temperature and can control the temperature of external instruments. Refrigerated or cooling water baths allow operation below ambient temperature, while oil baths extend the usable range above 100°C for high-temperature applications. Safety features often include over-temperature protection, low-water-level cutoff to prevent dry heating, and alarms for temperature deviation. Removable racks and floating holders accommodate test tubes, flasks, and microplates of various sizes.
Common applications include incubating cultures, running enzyme reactions, thawing samples, warming reagents, maintaining assay temperatures, and serving as a heat source for rotary evaporators. To ensure reliable performance, water should be changed regularly to prevent algae growth and mineral buildup, distilled water is recommended to reduce scale, and temperature sensors should be calibrated periodically. Overall, the water bath is a simple, reliable, and versatile tool for precise temperature control in the laboratory.