Water Quality Monitoring for Science Exhibitions: Build Guide

Water quality is one of the most compelling science exhibition topics for Indian students — it connects directly to public health, the Jal Jeevan Mission, and everyday life. A portable water quality monitor that measures pH, TDS (total dissolved solids), turbidity, and temperature can test school drinking water, local river water, and borewell water — generating real scientific data that has genuine community value.

This guide walks you through building a multi-parameter water quality monitor for science exhibitions, with calibration procedures, data logging, and presentation ideas that consistently impress judges at district and state-level exhibitions.

Why Water Quality Matters in India

India faces significant water quality challenges: according to NITI Aayog, approximately 60 crore people face high to extreme water stress, and waterborne diseases account for 3.8 crore cases of illness annually. BIS standard IS 10500 sets drinking water limits: TDS below 500 mg/L (desirable) or 2000 mg/L (permissible), turbidity below 1 NTU (desirable), pH 6.5-8.5.

Testing school water, local borewell, municipal tap, and nearby water bodies with your sensor and comparing against IS 10500 gives your project immediate community relevance — and gives judges a clear understanding of real-world impact.

Parameters to Measure

TDS Sensor Setup and Code

TDS (total dissolved solids) is measured by the electrical conductivity of water — more dissolved minerals means higher conductivity. A gravity TDS probe with Arduino reads conductivity and converts to mg/L (ppm):

#define TDS_PIN A0
#define VREF 5.0
#define SCOUNT 30  // Number of samples

int analogBuffer[SCOUNT];
int analogBufferIndex = 0;

float readTDS() {
  // Collect samples
  for (int i = 0; i < SCOUNT; i++) {
    analogBuffer[i] = analogRead(TDS_PIN);
    delay(40);
  }

  // Median filter
  int temp;
  for (int i = 0; i < SCOUNT-1; i++)
    for (int j = i+1; j < SCOUNT; j++)
      if (analogBuffer[i] > analogBuffer[j]) {
        temp = analogBuffer[i];
        analogBuffer[i] = analogBuffer[j];
        analogBuffer[j] = temp;
      }
  int medianVal = analogBuffer[SCOUNT/2];

  float voltage = medianVal * (VREF / 1023.0);
  // Temperature compensation (25 degrees C reference)
  float compensatedVolt = voltage / (1.0 + 0.02 * (25.0 - 25.0));
  float tdsValue = (133.42 * pow(compensatedVolt, 3)
                   - 255.86 * pow(compensatedVolt, 2)
                   + 857.39 * compensatedVolt) * 0.5;
  return tdsValue;
}

Calibrate by dissolving a known amount of table salt in a measured volume of distilled water and comparing your reading to the theoretical value. At 25°C, 1 gram of NaCl in 1 litre of distilled water gives approximately 1000 ppm TDS.

Turbidity Measurement

Turbidity measures how much light is scattered by suspended particles. A simple DIY turbidity sensor uses an infrared LED and photodetector on opposite sides of a water-filled cuvette:

#define TURBIDITY_PIN A1

float readTurbidity() {
  int reading = analogRead(TURBIDITY_PIN);
  float voltage = reading * (5.0 / 1023.0);

  // Calibration: clear water ~4.2V, muddy water ~2.5V
  // Convert to NTU (approximate, for demonstration)
  float ntu;
  if (voltage >= 4.2) ntu = 0;           // Clear water
  else if (voltage < 2.5) ntu = 3000;    // Very turbid
  else ntu = map(voltage*100, 250, 420, 3000, 0) / 100.0;

  return ntu;
}

For more accuracy, calibrate against known turbidity standards: distilled water (0 NTU), milk dilutions (calibrate empirically), and filtered sediment samples from your local river or well.

Data Logging to SD Card

Log readings with timestamps using an SD card module and DS3231 RTC for a permanent record:

#include <SD.h>
#include <RTClib.h>

RTC_DS3231 rtc;

void logReading(float tds, float turbidity, float temp) {
  DateTime now = rtc.now();
  File f = SD.open("wqlog.csv", FILE_WRITE);
  if (f) {
    f.print(now.timestamp());
    f.print(",");
    f.print(tds); f.print(",");
    f.print(turbidity); f.print(",");
    f.println(temp);
    f.close();
  }

  // Display on LCD
  lcd.clear();
  lcd.print("TDS:"); lcd.print((int)tds); lcd.print("ppm");
  lcd.setCursor(0, 1);
  lcd.print("Turb:"); lcd.print(turbidity, 1); lcd.print("NTU");
}

Over several weeks, collect readings from multiple sources: school drinking water tap, school borewell (if present), a local river or pond, and commercially sold packaged water as a control. Export the CSV to Excel and create bar charts for comparison.

Exhibition Presentation Ideas

To maximise your exhibition impact:

• Live demonstration: Bring three water samples in clear bottles — school tap water, purchased mineral water, and visibly turbid water. Show judges real-time readings as you dip the probe in each.
• Comparison poster: Bar charts comparing your measured values against BIS IS 10500 drinking water standards. Red bars for values exceeding limits.
• Map visualisation: If you tested multiple water sources in your town, plot them on a local map with colour-coded quality indicators.
• Cost comparison: Your Rs. 1,500 sensor vs commercial water quality testers (Rs. 15,000-50,000) — accessible technology for communities that cannot afford professional testing.
• Recommendations: Based on your data, propose specific interventions (boiling, RO filter, UV treatment) for each water source.

Frequently Asked Questions

How accurate is an Arduino TDS sensor compared to a laboratory measurement?

The gravity TDS probe with proper calibration achieves approximately 10-15% accuracy — sufficient for comparative studies and science fair purposes. Laboratory instruments use four-electrode conductivity cells with temperature compensation achieving 1-2% accuracy. For exhibition purposes, acknowledge this limitation and focus on relative comparisons rather than absolute values.

Can I measure pH without a laboratory-grade electrode?

Yes — the DFRobot pH sensor (Rs. 600-800 from Indian electronics suppliers) uses a glass membrane electrode and provides 0.1 pH unit accuracy with proper calibration using pH 4.0 and pH 7.0 buffer solutions (available from laboratory suppliers or online). This is sufficient for exhibition-grade measurements.

My school is near Ganga/Yamuna/Godavari. Can I test river water?

Yes, and this makes your project highly relevant. Compare river water TDS, turbidity, and pH at different distances from industrial areas or sewage outfalls. Documenting water quality variations along a river is a compelling exhibition topic with genuine environmental monitoring value.

Do I need permission to collect water samples for testing?

For water from public sources (rivers, public taps), no special permission is required. For school water systems, obtain the principal’s permission and involve the science teacher. For private borewells or industrial outlets, ask the owner. Always test in supervised conditions and never drink water tested in your project setup.