A prototype of water level detection has been designed using the HC-SR04 sensor and the GSM SIM800L module based on the ATMega328 Microcontroller. This study aims to monitor the water level through indication media such as LED colors and different buzzer sounds. In addition, the communication medium between the user and the design tool is using SMS. Users can also control the Relay and provide information in the form of current water levels via SMS. The components used to design this system are Arduino Uno, sensor HC-SR04, GSM SIM800L Module, LCD, LED, buzzer and Step-Down regulator. The principle of this system is the system will indicate the water level through predetermined statuses, such as safe, alert and dangerous. Each status has a different LED color and buzzer sound. When the water level reaches the threshold value for each status, the design tool will send a message to the user in the form of the current status and water level. When the water level reaches dangerous status, the relay will turn on and off when the water level reaches safe status. Based on the standard deviation value, the designed tool has a fairly small standard deviation between 0-0.2 cm so that the tool is said to be quite precision. Meanwhile, based on the results of the calibration test between the read distance on the LCD and the ruler, the coefficient of determination is 0.9996 or 99.96% and SMS with the ruler obtained 0.9997 or 99.97%. This indicated that the designed tool has good accuracy.