Technology to optimize the potential of rainwater that utilizes rainwater harvesting technology (PAH) cannot simply be accepted by the community, especially in urban areas. Urban areas have limited land to support rainwater storage which has large dimensions with the shape of a tube. Therefore, a modular form was developed that can help urban communities who do not have large lands to optimize the potential for rainwater that falls and is used as clean water to supply daily needs. These components are collected and classified according to urban infrastructure systems (UIS). The planned reservoir with dimensions that are more effective and easy to apply in various places is planned to have a maximum dimension of 1 meter high and 0.5 meters wide made of modular plastic. After going through the stages of analysis of the discharge that can be accommodated in the engineering of a modular rainwater reservoir, then proceed with the design process and provide clarity of designation examples. By utilizing the form with a capacity of 32 liters, this rainwater reservoir can be arranged and adjusted according to the designation of the people who want to use it.

The availability of water is difficult to measure accurately, causing delays in water supply for the community, so a monitoring tool is needed that can provide accurate and real-time information to measure water availability so that clean water can be distributed to areas that need it on time. The digital indicator developed in this study by adding a water tank system with an ultrasonic sensor HC-SR04 to detect the water level. The working principle of this sensor is that the ECHO pin emits a wave and the TRIG pin is triggered on the reflected wave which is then reflected back so that the obstacle distance can be measured by calculating the time between the emission and the reflected wave. The procedure for installing the sensor on the reservoir is done by installing the sensor on the top side of the tank vertically and there is no media barrier, then water enters with a constant flow rate (m 3 /s), and sensor data is recorded by reading the water level (m) which is then converted into unit volume of water (m 3 ). The Blynk Android application is used as a user interface and monitoring. Water availability monitoring is displayed in a three-color graphic display, green, yellow, and red. Green indicates that the water supply is sufficient (safe level), yellow indicates that the water is insufficient (warning level), red indicates that the water supply is running low or and needs to be refilled immediately to meet the required availability.