Water electrolysis system and water level error calculation apparatus

A water electrolysis system, comprising:

• a water electrolyzer configured to electrolyze water to generate gas including oxygen and hydrogen;
• a gas-liquid separator configured to separate a gas phase including hydrogen from a liquid phase of the gas generated by the water electrolyzer;
• a water level detector configured to detect a water level in the gas-liquid separator;
• a pressure detector configured to detect a pressure of the gas phase in the gas-liquid separator;
• and
• a CPU and a memory coupled to the CPU, wherein
• the CPU is configured to function as:
• an arithmetic unit configured to calculate an error of the water level in the gas-liquid separator detected by the water level detector based on the pressure of the gas phase in the gas-liquid separator detected by the pressure detector, to calculate the pressure of the gas phase in the gas-liquid separator based on an amount of hydrogen generated by the water electrolyzer and the water level in the gas-liquid separator detected by the water level detector, and to calculate the error of the water level in the gas-liquid separator detected by the water level detector based on the pressure of the gas phase calculated and the pressure of the gas phase detected by the pressure detector.