Arduino Water Level Display: Show Tank Level on an I2C LCD

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An Arduino water-level display combines a sensor, an Arduino Uno, and a 16×2 or 20×4 character LCD. The sensor may send an analog signal to A0, while the LCD uses the Uno’s I2C bus on A4 (SDA) and A5 (SCL). The Arduino calibrates the sensor’s raw reading and displays a normalized percentage, estimated height, and status such as LOW, MEDIUM, or HIGH.

This guide builds the simplest version with a conductive analog sensor, then explains when a waterproof ultrasonic or non-contact capacitive sensor is a better choice for a tank or permanent installation.

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How the water-level display works

Water-level sensor → Arduino input → calibration and filtering → percentage/status
                                      ↓
                                I2C LCD display

The display can show several different meanings of “level”:

• Raw sensor value: the ADC number returned by analogRead().
• Normalized level: a calibrated value from 0 to 100 percent.
• Physical height: an estimated water height in centimetres.
• Tank fullness: a percentage based on measured empty and full conditions.
• Threshold status: a label such as LOW, MEDIUM, or HIGH.

A raw Arduino reading is not automatically a percentage. Calibration is required, and a level percentage is not necessarily a true volume percentage in an irregular or horizontal tank.

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Choose the right sensor

Conductive analog sensor

A typical inexpensive probe module exposes conductive traces to the water and produces an analog signal. It is easy to connect and suitable for open containers, short experiments, and learning projects. Its reading changes with water conductivity, immersion depth, orientation, supply voltage, and sensor construction. The exposed traces can also corrode, especially when continuously powered with DC.

Use this type as an educational sensor rather than a precision or unattended tank instrument. An example Arduino project uses a water sensor on an analog input with an I2C LCD: Arduino Project Hub Smart Dispenser.

Waterproof ultrasonic sensor

An ultrasonic sensor measures the distance from a transducer above the tank to the water surface. A waterproof Arduino-listed sensor is specified for 3.0–5.5 V operation, a 20 cm to 6 m operating range, 1 mm stated resolution, and 30 mA operating current. Those specifications apply to that particular model, not to every HC-SR04-style module. See the manufacturer’s product page.

As the tank fills, the measured distance decreases:

waterHeight = emptyDistance - measuredDistance
levelPercent = 100 × waterHeight / usableTankHeight

Mount the sensor vertically above the maximum water level. Foam, splashing, condensation, turbulence, narrow walls, and the sensor’s minimum range can cause false or unstable readings. A bare indoor HC-SR04 is not waterproof.

Non-contact capacitive sensor

A non-contact sensor can detect liquid through a container wall, making it useful for sealed containers or liquids that should not touch a probe. The Arduino Gravity model is described as using the XKC-Y25-T12V signal-processing chip, but it is a digital level detector, not automatically a continuous analog height sensor. Confirm the module’s output behaviour before designing a multi-level percentage display. See the Arduino product description.

Parts for the beginner circuit

• Arduino Uno Rev3 or compatible 5 V board
• 16×2 I2C character LCD
• Analog water-level sensor
• Breadboard and jumper wires
• USB cable and Arduino IDE

A 20×4 LCD is useful when you want to show raw value, percentage, height, and alarm state together. Keep the Arduino and LCD electronics above the tank and protected from splashes.

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Wire the sensor and I2C LCD

On an Arduino Uno Rev3, use this wiring:

The LCD’s I2C connection and the sensor’s signal connection are separate. “I2C LCD” does not mean that the water sensor also communicates over I2C. Nano boards based on the same ATmega328P arrangement typically use A4 and A5 too, but other Arduino families may expose I2C on different labelled pins. Check the board pinout.

Confirm that the module labels mean VCC, ground, and signal. A 3.3 V board may not tolerate a 5 V sensor or LCD pull-up; verify voltage limits and use level shifting where necessary.

Find the LCD address

0x27 is common, but it is not universal. Some backpacks use 0x3F or another address. Upload this scanner before troubleshooting the LCD:

#include <Wire.h>

void setup() {
  Serial.begin(9600);
  Wire.begin();
  Serial.println("I2C scanner");

  for (byte address = 1; address < 127; address++) {
    Wire.beginTransmission(address);
    byte error = Wire.endTransmission();

    if (error == 0) {
      Serial.print("Found I2C device at 0x");
      if (address < 16) Serial.print("0");
      Serial.println(address, HEX);
    }
  }
}

void loop() {}

Open the Serial Monitor at 9600 baud. If it reports 0x3F, replace 0x27 in the LCD object. If it finds nothing, check power, common ground, SDA/SCL orientation, solder joints, and cable length.

Install a compatible LCD library

In Arduino IDE, open Tools → Manage Libraries and install the exact library required by your sketch. Arduino documents similarly named libraries including LiquidCrystal_I2C, LCD-I2C, and LiquidCrystal I2C. Their APIs are not guaranteed to be interchangeable.

The sketch below targets a common LiquidCrystal_I2C API. If lcd.init() does not compile, open the installed library’s example and use its initialization form, which may be lcd.begin(16, 2) or lcd.begin().

Calibrate empty and full readings

1. Remove the sensor from the water, or place it at the defined empty position.
2. Open the Serial Monitor and record the stable empty reading.
3. Place the sensor at the intended full-water position.
4. Record the stable full reading.
5. Replace EMPTY_READING and FULL_READING in the sketch.
6. Test several intermediate levels.
7. Confirm whether the value rises or falls as the water rises.

The calculation is:

percentage = 100 × (raw − emptyReading) / (fullReading − emptyReading)

The result is clamped to 0–100 so readings outside the calibration points do not produce impossible percentages. Calibration values from another sensor or another liquid should not be copied.

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Complete Arduino sketch

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const byte SENSOR_PIN = A0;

// Replace 0x27 with the address found by the scanner.
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Replace these with your measured calibration values.
const int EMPTY_READING = 120;
const int FULL_READING  = 760;
const byte SAMPLE_COUNT = 10;

int readAveragedSensor() {
  long total = 0;

  for (byte i = 0; i < SAMPLE_COUNT; i++) {
    total += analogRead(SENSOR_PIN);
    delay(5);
  }

  return total / SAMPLE_COUNT;
}

void setup() {
  Serial.begin(9600);

  lcd.init();       // Some libraries use lcd.begin() instead.
  lcd.backlight();
  lcd.clear();

  lcd.setCursor(0, 0);
  lcd.print("Water level");
  delay(1000);
}

void loop() {
  int raw = readAveragedSensor();

  int percent = map(raw, EMPTY_READING, FULL_READING, 0, 100);
  percent = constrain(percent, 0, 100);

  const char* status;

  if (percent < 30) {
    status = "LOW";
  } else if (percent < 70) {
    status = "MEDIUM";
  } else {
    status = "HIGH";
  }

  lcd.setCursor(0, 0);
  lcd.print("Level: ");
  if (percent < 100) lcd.print(" ");
  if (percent < 10)  lcd.print(" ");
  lcd.print(percent);
  lcd.print("% ");

  lcd.setCursor(0, 1);
  lcd.print("Status: ");
  lcd.print(status);
  lcd.print("       ");

  Serial.print("Raw: ");
  Serial.print(raw);
  Serial.print("  Level: ");
  Serial.print(percent);
  Serial.print("%  Status: ");
  Serial.println(status);

  delay(500);
}

The display refreshes twice per second, which is “real-time” only in the practical hobby-project sense of repeatedly updating the reading. It does not make the sensor industrially accurate or suitable for safety-critical control.

Display height instead of—or as well as—percentage

If the calibrated usable tank height is known, convert the normalized result to an estimated height:

const float TANK_HEIGHT_CM = 35.0;
float heightCm = (percent / 100.0) * TANK_HEIGHT_CM;

For a 16×2 display, replace the second-line output with:

lcd.setCursor(0, 1);
lcd.print(heightCm, 1);
lcd.print(" cm        ");

This is an estimate based on empty/full calibration. It is not a direct physical measurement unless the sensor and installation are designed and calibrated for that purpose.

If the sensor value decreases as the water rises, reverse the mapping:

int percent = map(raw, FULL_READING, EMPTY_READING, 100, 0);
percent = constrain(percent, 0, 100);

Improve stability and reliability

Reduce noisy readings

The example averages ten samples. For more difficult signals, use a moving median or an exponential filter:

filtered = (filtered * 0.8) + (newReading * 0.2);

Filtering smooths the display; it does not correct poor calibration, corrosion, bad placement, or a sensor that is unsuitable for the liquid.

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• The sensor has a DIP switch. The DIP switch controls the output voltage (high level) of the signal terminal (green line). When the DIP switch is dialed to 5V, the high level is 5V. When the DIP switch is dialed At 3V, the high level is 3.3V.
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Prevent status flicker

Use hysteresis around thresholds. For example, change to LOW below 25 percent, but do not leave LOW until the reading exceeds 30 percent. This prevents small fluctuations from repeatedly changing the displayed status.

Limit conductive-probe corrosion

• Power the probe only while taking a reading.
• Sample infrequently rather than continuously.
• Consider alternating polarity instead of applying continuous DC.
• Use a capacitive or ultrasonic sensor for a permanent installation.

These measures may slow corrosion; they do not turn an inexpensive conductive probe into a long-term precision instrument.

Handle tank turbulence

For ultrasonic measurement, average multiple readings, reject impossible jumps, use a stilling tube or calm section where appropriate, and avoid measuring immediately after a pump starts or stops. If no valid echo is received, display ERR or NO ECHO rather than a false percentage.

Ultrasonic sensor alternative

The LCD wiring and library remain the same, but the sensor input changes from analogRead() to trigger-and-echo timing:

const byte TRIG_PIN = 9;
const byte ECHO_PIN = 10;

unsigned long duration;
float distanceCm;

digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(2);
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);

duration = pulseIn(ECHO_PIN, HIGH, 30000UL);

if (duration == 0) {
  // No echo received: treat the reading as invalid.
} else {
  distanceCm = duration * 0.0343 / 2.0;
}

const float EMPTY_DISTANCE_CM = 80.0;
const float FULL_DISTANCE_CM  = 15.0;

float levelPercent =
  100.0 * (EMPTY_DISTANCE_CM - distanceCm) /
  (EMPTY_DISTANCE_CM - FULL_DISTANCE_CM);

levelPercent = constrain(levelPercent, 0.0, 100.0);

The subtraction is reversed because a fuller tank produces a smaller distance. Replace the empty and full distances with measurements from the actual installation, and ensure the tank fits within the sensor’s specified range.

Troubleshooting

The LCD is blank

1. Run the I2C scanner and verify the address.
2. Check SDA and SCL wiring.
3. Confirm power and common ground.
4. Turn the backpack contrast potentiometer slowly.
5. Test a minimal “Hello” LCD sketch.
6. Check whether your library requires init() or begin().

The LCD shows blocks only

Power and contrast are probably present, but initialization is failing. Check the address, library compatibility, backpack soldering, SDA/SCL wiring, and board voltage.

The percentage is wrong

Recalibrate empty and full conditions. Check sensor orientation, immersion depth, supply voltage, water conductivity, and whether the reading rises or falls with water level. A copied calibration number is rarely reliable.

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The status flickers

Increase averaging, slow the display update, or add hysteresis to the thresholds.

The ultrasonic sensor reports no echo

Check the trigger and echo pins, timeout handling, mounting angle, minimum range, condensation, foam, and whether the beam is striking a tank wall.

The displayed percentage does not equal volume

In a cylindrical vertical tank, height and volume may be approximately proportional. In a horizontal cylinder or irregular reservoir, they are not. For accurate volume, create a calibration table that maps measured height to actual volume.

When to upgrade the design

Keep the conductive analog sensor for a quick demonstration or short-term open-container project. For a tank, outdoor installation, or non-contact requirement, a waterproof ultrasonic sensor is usually the more suitable hobby upgrade. A non-contact capacitive detector is useful when you need a sealed-wall point-level signal, but verify that it can provide the continuous data your display requires.

For unattended, chemically aggressive, drinking-water, industrial, or safety-critical applications, use a properly rated sensor and enclosure. Do not connect a mains pump directly to an Arduino. Pump automation requires an appropriately rated relay or MOSFET, fuse, flyback protection where applicable, isolation, enclosure, and safe mains wiring.

The project concept—reading a water-level sensor and presenting a normalized value and status on an I2C LCD—is also demonstrated by Visuino’s Arduino water-level display project. The key engineering decisions remain sensor selection, calibration, installation, and handling invalid readings.

Quick Recap

Bestseller No. 1

DIYables Water Sensor Detector for Arduino, ESP32, ESP8266, Raspberry Pi, 5 Pieces

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

$5.99

Bestseller No. 2

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Bestseller No. 3

CQRobot Capacitive Non-Contact Liquid Level Sensor for Arduino Raspberry Pi

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Bestseller No. 4

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Bestseller No. 5

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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.