A practical ESP32 water-level system uses a sensor to measure the air gap above the water, converts that measurement into depth and percentage, and optionally controls a pump. For most household tanks and low-voltage prototypes, a waterproof ultrasonic sensor such as a JSN-SR04T is the most useful primary sensor. For automatic pumping, add an independent float switch: ultrasonic sensing provides continuous level information, while the float switch provides a separate safety interlock.
This design is suitable for monitoring overhead tanks, reservoirs, sumps, rainwater tanks, and similar installations. It is a prototype design, not certified industrial instrumentation. Permanent mains-pump wiring should be installed and tested by a qualified electrician.
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How an ESP32 water-level system works
An ultrasonic sensor does not directly measure “percentage full.” It measures the distance between its transducer and the water surface.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitches- Air gap: distance from the sensor to the water.
- Water depth: tank reference height minus the measured air gap.
- Level percentage: the usable depth normalized between calibrated empty and full points.
- Volume percentage: requires the shape of the tank to be considered.
The basic calculation is:
waterDepth = tankHeight - measuredAirGapFor a calibrated system, use:
levelPercent = 100 × (emptyAirGap - airGap) / (emptyAirGap - fullAirGap)Clamp the result between 0 and 100 percent. A rectangular or vertical cylindrical tank has an approximately constant cross-section, so depth percentage is close to volume percentage. For a horizontal cylinder, cone, irregular tank, or tank with internal obstructions, use a tank-specific lookup table or calibration curve if volume accuracy matters.
#1 Best Overall
- Used to detect the presence of water, water leakage
- Used to measure the water level
- Supply voltage: 3.3 - 5V DC. Current consumption: less than 20mA
- Water sensor for Arduino, ESP32, ESP8266, Raspberry Pi, or any 5V or 3.3V microcontroller.
- Tutorials for Arduino, ESP32, ESP8266 and Raspberry Pi are provided => search for: DIYables Water Sensor
Recommended system architecture
Monitoring-only version
Waterproof ultrasonic sensor → ESP32 → OLED, serial output, or Wi-Fi dashboardThis version can display the level, send low-level and overflow alerts, and publish readings to a local web page, MQTT broker, Home Assistant installation, or other dashboard. The local measurement should continue even if Wi-Fi is unavailable.
Automatic pump version
Tank ultrasonic sensor ─┐
├→ ESP32 → isolated relay or contactor → pump
Source-tank float ─────┘Recommended behavior is to start filling below a low threshold, stop at a higher threshold, refuse to start when the source tank is empty, and switch the pump off on an overflow alarm, invalid sensor reading, or excessive runtime.
Choosing the level sensor
| Sensor | Best use | Advantages | Limitations |
|---|---|---|---|
| Waterproof ultrasonic | Continuous tank monitoring | Non-contact and easy to interface | Foam, turbulence, condensation, blind zone, and reflections can cause errors |
| HC-SR04 | Dry indoor demonstrations | Cheap and widely supported | Not waterproof; its echo may require level shifting |
| Float switch | Overflow, low-level, and dry-run protection | Simple, independent, and inexpensive | Binary measurement; mechanical parts can stick |
| Conductive probe | Low-cost point or multi-level detection | Simple analog or digital output | Electrolysis, corrosion, deposits, and water-conductivity dependence |
| Capacitive sensor | Sealed or corrosive tanks | No exposed electrodes; may work through a tank wall | Requires careful calibration and mounting |
| Pressure sensor | Deep, foamy, or turbulent tanks | Continuous measurement unaffected by surface echoes | Immersed sensor, sealing requirements, drift, and more complex conditioning |
JSN-SR04T waterproof ultrasonic sensor
A JSN-SR04T-style module uses a remote waterproof transducer and trigger/echo interface. One published specification gives an approximate range of 25–600 cm, but minimum range, operating mode, and electrical behavior vary between module revisions and suppliers. Check the exact board and datasheet before designing around those numbers: JSN-SR04T wiring and specifications and module timing information.
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Mount the transducer perpendicular to the water surface, away from inlet jets, braces, pipes, cables, and tank walls. Foam, steam, condensation, and turbulence may produce missing or false echoes. Leave sufficient clearance above the full-water point because ultrasonic sensors have a blind zone near the transducer.
Some product listings claim 3.0–5.5 V operation, but that claim applies to the particular product, not every JSN-SR04T board. The exact echo-output voltage must be confirmed. A product example is available from Circuit Rocks.
HC-SR04
The HC-SR04 is suitable for a dry indoor prototype, not a damp or splash-prone tank installation. A representative ESP32 example is documented at ESP32 ultrasonic sensor tutorial. If the module is powered at 5 V, do not assume its echo output is safe for an ESP32 GPIO.
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Float switches
Use a float switch as an independent source-empty, high-level, or overflow interlock. A normally closed switch is often preferable for fault detection because a broken wire can be treated as an unavailable or unsafe condition, although the final choice depends on the installation and control circuit. Two switches—one for minimum source level and one for maximum destination level—can provide more dependable pump protection than ultrasonic readings alone.
Parts required
- ESP32 development board.
- Waterproof ultrasonic sensor for humid or outdoor tanks.
- Regulated 5 V supply for the sensor, if required by the module.
- Suitable 3.3 V supply for the ESP32.
- Voltage divider or logic-level shifter for an echo signal above 3.3 V.
- Optional I2C OLED display.
- Optional normally closed float switch or switches.
- Appropriately isolated relay or contactor interface.
- Fuse, enclosure, cable glands, strain relief, terminal blocks, and suitable wiring.
ESP32 wiring
For a classic ESP32 DevKit-style board, these are example assignments:
JSN-SR04T VCC → regulated 5 V
JSN-SR04T GND → ESP32 GND
JSN-SR04T TRIG → GPIO 5
JSN-SR04T ECHO → GPIO 18 through a voltage dividerThe pins are examples, not universal requirements. Protect any echo signal that can exceed the ESP32’s GPIO tolerance. Espressif specifies GPIO voltage tolerance of 3.6 V: ESP32 hardware guidance.
For a nominal 5 V echo, an example divider is:
Sensor ECHO ── 1 kΩ ──┬── ESP32 GPIO
│
2 kΩ
│
GNDThis produces approximately 3.33 V from a 5 V input. Use a proper level shifter where cable length, noise, speed, or product reliability makes it preferable.
Take care with pin selection. GPIO34–GPIO39 on the original ESP32 are input-only and lack software pull-ups and pull-downs. GPIO6–GPIO11 are normally connected to flash. Strapping pins have boot-time restrictions. These details vary across ESP32 families, so consult the relevant Espressif pin guidance before finalizing the PCB.
For a float switch, connect one side to ground and the other to a suitable input configured with INPUT_PULLUP, provided that pin supports the required pull-up. The software must define whether an open or closed switch means “safe.”
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Install Arduino-ESP32 support
- Install Arduino IDE.
- Open Boards Manager.
- Install esp32 by Espressif Systems.
- Select the board profile matching the actual hardware.
- Select the correct serial port.
- Upload a simple serial test before connecting pump hardware.
The current Arduino-ESP32 documentation identifies version 3.3.10, based on ESP-IDF 5.5, but installed versions and supported board profiles change. Verify the current documentation when setting up: Arduino-ESP32 documentation and installation guide.
Basic ultrasonic test sketch
const int TRIG_PIN = 5;
const int ECHO_PIN = 18;
float readDistanceCm() {
digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(3);
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
unsigned long duration = pulseIn(ECHO_PIN, HIGH, 30000UL);
if (duration == 0) return NAN;
return duration * 0.0343f / 2.0f;
}
void setup() {
Serial.begin(115200);
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
digitalWrite(TRIG_PIN, LOW);
}
void loop() {
float distanceCm = readDistanceCm();
if (isnan(distanceCm)) {
Serial.println("Sensor timeout");
} else {
Serial.print("Air gap: ");
Serial.print(distanceCm, 1);
Serial.println(" cm");
}
delay(1000);
}The formula divides by two because the sound travels to the water and back:
distanceCm = echoTimeMicroseconds × 0.0343 / 2Filtering and percentage conversion
Never let one raw ultrasonic reading switch a pump. Take several readings, reject impossible values, and use a median or trimmed mean when occasional spikes occur.
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const int ECHO_PIN = 18;
const float EMPTY_AIR_GAP_CM = 140.0f;
const float FULL_AIR_GAP_CM = 20.0f;
float readDistanceCm() {
digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(3);
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
unsigned long duration = pulseIn(ECHO_PIN, HIGH, 30000UL);
if (duration == 0) return NAN;
return duration * 0.0343f / 2.0f;
}
float readFilteredDistanceCm() {
const int samples = 7;
float values[samples];
int valid = 0;
for (int i = 0; i < samples; i++) {
float value = readDistanceCm();
if (!isnan(value) && value > 2.0f && value < 600.0f) {
values[valid++] = value;
}
delay(70);
}
if (valid == 0) return NAN;
float total = 0.0f;
for (int i = 0; i < valid; i++) total += values[i];
return total / valid;
}
float distanceToPercent(float airGapCm) {
float percentage = 100.0f *
(EMPTY_AIR_GAP_CM - airGapCm) /
(EMPTY_AIR_GAP_CM - FULL_AIR_GAP_CM);
return constrain(percentage, 0.0f, 100.0f);
}
void setup() {
Serial.begin(115200);
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
digitalWrite(TRIG_PIN, LOW);
}
void loop() {
float airGap = readFilteredDistanceCm();
if (isnan(airGap)) {
Serial.println("FAULT: no valid ultrasonic reading");
delay(1000);
return;
}
Serial.print("Air gap: ");
Serial.print(airGap, 1);
Serial.print(" cm, level: ");
Serial.print(distanceToPercent(airGap), 1);
Serial.println("%");
delay(1000);
}EMPTY_AIR_GAP_CM and FULL_AIR_GAP_CM are example values only. They must be replaced with measurements from the installed tank.
Calibrate the tank
- Mount the sensor in its final position.
- Measure from the sensor’s reference point, not merely from the tank lid.
- Record the reading at the desired empty cutoff.
- Fill the tank to the desired full cutoff and record the second reading.
- Store those readings in the firmware.
- Check several intermediate levels against a physical measurement.
- Create a lookup table if the required result is volume rather than depth.
Do not use nominal tank height blindly. The tank may have a curved bottom, the sensor may sit above the lid, and the pump may need to stop before the physical top. Keep the transducer away from turbulence and ensure the full-level target remains outside the sensor’s blind zone. A stilling tube can help with a moving or foamy surface.
Automatic pump control
Use hysteresis
Use separate start and stop thresholds so small measurement changes do not cause relay chatter:
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const float PUMP_START_PERCENT = 30.0f;
const float PUMP_STOP_PERCENT = 85.0f;Conceptually:
if level < 30%: pump ON
if level > 85%: pump OFFAdd independent interlocks
A robust controller should include:
- Source-tank float switch to prevent dry running.
- Independent high-level overflow cutoff.
- Maximum continuous pump runtime.
- Minimum off-time between starts.
- Sensor timeout and plausibility checks.
- Manual override with a clear safe state.
- Defined behavior after power loss.
- Hardware emergency cutoff where consequences of overflow are serious.
A conservative state machine can include FAULT, IDLE, FILLING, FULL, SOURCE_EMPTY, and TIMEOUT. On an invalid reading or an unavailable source, the pump should turn off. Wi-Fi must not be required for local safety.
Relay and mains safety
An ESP32 GPIO cannot drive a pump motor directly.
For a low-voltage DC pump, use a correctly rated MOSFET or relay, a flyback diode for relay coils or inductive DC loads, and wiring sized for the pump current. Confirm that the relay input reliably recognizes 3.3 V.
For an AC pump, use an appropriately rated relay, contactor, or solid-state device. Consider motor starting current, inductive-load ratings, fusing, grounding, enclosure, isolation, creepage, and clearance. Do not put mains terminals on a breadboard. A relay module advertised as “30 A” is not automatically suitable for a motor or household installation.
Keep water and mains wiring physically separated, use cable glands and strain relief, and install the electronics in a suitable enclosure. Have permanent household wiring completed or checked by a qualified electrician.
Wi-Fi monitoring without compromising control
The ESP32 can publish level data through a local web server, MQTT, Home Assistant, a cloud dashboard, or an ESP-NOW link to another ESP32. These are monitoring and convenience features, not safety mechanisms.
When Wi-Fi fails, the controller should continue local measurement and local control if readings remain valid. If the sensor becomes invalid for a defined period, switch the pump off. Reconnect with backoff rather than blocking the control loop.
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- Dual Output Format: Offers both digital switch output (0 and 1) for easy integration into digital circuits and analog AO voltage output for more precise measurements and applications.
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If you use an analog sensor on the original ESP32, prefer ADC1 when Wi-Fi is active. ADC2 has limitations during Wi-Fi operation. See Espressif’s hardware design guidance and ADC documentation.
Conductive and analog sensor cautions
Conductive probes should be powered only during measurement where possible. A representative ESP32 example powers the sensor briefly, reads the ADC, then turns it off: conductive water-sensor example.
Raw ADC values are not precision voltage measurements. On the original ESP32, the nominal ADC reference is 1.1 V, but actual reference values can vary approximately from 1.0 to 1.2 V between chips. Use calibration when converting ADC readings to voltage: Espressif ADC calibration. A calibrated percentage map for one tank is different from an accurate, repeatable industrial measurement.
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Troubleshooting
No echo, zero, or maximum distance
- Check sensor power, ground, trigger, and echo wiring.
- Confirm the software pin assignments.
- Test against a fixed object at a known distance.
- Install the required divider or level shifter.
- Check whether the water surface is inside the blind zone.
- Confirm the exact sensor revision and timing mode.
Erratic readings
- Use a median or trimmed-mean filter.
- Increase the interval between readings.
- Reduce turbulence and foam with a stilling tube.
- Move the transducer away from walls and obstructions.
- Separate sensor and pump wiring.
- Improve grounding, decoupling, and power regulation.
- Reject readings outside the physically possible range.
ESP32 resets when the pump starts
Likely causes include voltage sag, relay-coil current, motor EMI, poor grounding, or inadequate isolation. Use appropriately separate supplies where necessary, an isolated switching interface, load-appropriate suppression, and decoupling near the ESP32. Keep high-current motor returns out of the ESP32 ground path.
Analog readings change when Wi-Fi starts
Move the analog input from ADC2 to ADC1 on the original ESP32. Also check attenuation, calibration, sensor supply stability, and the selected board’s pin mapping. ESP32-C3, S3, and other variants do not have identical GPIO and ADC arrangements.
When to choose another sensor
Choose a pressure sensor when foam, vapor, or turbulence makes acoustic measurement unreliable and continuous level information is important. Choose capacitive sensing when the sensor must remain outside the liquid or the liquid is corrosive. Choose multiple float switches when the application needs dependable threshold protection rather than a percentage display. Conductive probes are useful for inexpensive demonstrations but require attention to corrosion, mineral deposits, liquid conductivity, and material suitability.
Practical limitations
- The ultrasonic system measures distance and derived depth, not volume unless tank geometry is modeled.
- Low-cost hobby sensors should not be presented as industrial instruments without appropriate testing and certification.
- Do not claim potable-water suitability without evidence for materials, hygiene, and certification.
- “Waterproof” depends on the exact probe, module, cable termination, and enclosure installation.
- Every ESP32 family has different pin, ADC, boot, and peripheral details.
- Pump protection exists only when the required independent interlocks and failure behavior have actually been implemented.
For a construction or home-automation prototype, the most balanced design is a calibrated waterproof ultrasonic sensor connected through a protected echo input, filtered firmware with timeouts, and a separate float switch for source-empty or overflow protection. Treat Wi-Fi as an optional reporting layer and treat mains switching as an electrical-installation task, not as an extension of the breadboard circuit.
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