RGDC Monitor: A Real-Time Rainwater TDS Tracking System

What is TDS?

Many of us have seen a pen-like device called a TDS meter to check water quality. When its electrodes are dipped into water, the display shows a number – the TDS value. For drinking water, this value is typically ideal between 50 to 300 ppm.

TDS means Total Dissolved Solids, referring to the total concentration of dissolved inorganic and organic substances in water. About 90–95% of these come from inorganic salts. Common ions contributing to TDS include:

  • Calcium (Ca²⁺)
  • Magnesium (Mg²⁺)
  • Sodium (Na⁺)
  • Potassium (K⁺)
  • Bicarbonates (HCO₃⁻)
  • Chlorides (Cl⁻)
  • Sulfates (SO₄²⁻)
  • Nitrates (NO₃⁻)
  • Phosphates (PO₄³⁻)

Pure water is a poor conductor of electricity. Conductivity increases when dissolved ions are present. A TDS meter actually measures the electrical conductivity (EC) of water in µS/cm. The TDS value is then estimated from EC (approximately EC × 0.55).

TDS in Rainwater

Rainwater forms by a natural distillation process – water evaporates from surface bodies and condenses into clouds. Ideally, distilled water should have zero TDS.

However, real rainwater rarely shows zero TDS because pollutants in the air dissolve in the tiny droplets. Urban and industrial areas show significantly higher TDS due to vehicle emissions, dust, and industrial pollutants.

A recent study [1] reported rainwater electrical conductivity of:

  • 103.48 µS/cm in an industrial region of Delhi NCR
  • 70.87 µS/cm in a semi-urban area

This corresponds to TDS values of approximately 57 ppm and 39 ppm. Tracking rainwater TDS helps monitor pollution levels and contributes to climate studies.

RGDC Monitor at Ramanuj Gupta Degree College

To monitor and study rainwater TDS in real time, Ramanuj Gupta Degree College, Silchar has developed the RGDC Monitor — an automated TDS collection and recording system. The system uploads its data online and can be downloaded from anywhere.

How the RGDC Monitor Works

1. Collector Unit

This unit collects fresh rainwater once sufficient rainfall occurs. The collected water flows into a measurement chamber where the TDS sensor is placed.

2. Sampling Unit

This electronic module:

  • records TDS readings from the sensor,
  • filters out noise using software algorithms,
  • averages the readings,
  • uploads the data with a timestamp via WiFi.

Users can access the data from the following public website:

Website: https://rgdcmonitor.blogspot.com

The project is fully Open Source (GNU GPL v3.0), and all technical details are available at:

GitHub: https://github.com/DwaipayanDeb/RGDC_Monitor

Since the installation was done only in late October 2025 — during low-rainfall months — few readings are currently available. Early measurements show a TDS as low as 7 ppm, which indicates low air pollution levels compared to Delhi NCR.

With long-term data collection, the RGDC Monitor will help analyze seasonal variations and long-term environmental trends.

References

  1. Singh, Y., Katoch, A., Yadav, S., Dhakad, S., Kulshrestha, U.C. (2024). Estimation of Non-Marine Fractions of Ions in Rainwater at Three Sites of Different Characteristics in Haryana State (India). Aerosol Air Qual. Res. 24, 230252. https://doi.org/10.4209/aaqr.230252
  2. Deb, D. (2025). Technical details for RGDC Monitor: Rainwater TDS Unit. Zenodo. https://doi.org/10.5281/zenodo.17515106

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