Home experiment – water purification

Home experiment 1 - Which water is actually best to drink?

Tap water, RO water, a bottle of mineral water: everyone has an opinion about which one is “best”. I decided to find out for myself, so I collected five kinds of water at home: tap water, RO (Reverse Osmosis) water, mineral water, seawater and rainwater. For each one I recorded the colour, odour, pH, sediment, how well soap lathered, and the TDS, or Total Dissolved Solids.

I wanted to find out which water is really the best, so I collected tap water from home, RO (Reverse Osmosis) water, mineral water, seawater and rainwater, and compared their colour, odour, pH, sediment, soap lather and TDS (Total Dissolved Solids). I was sure mineral water would win, but then I saw that our tap water measured 62 ppm TDS and the bottled water 243 ppm. I checked the labels twice, and for a few minutes I thought I had proved that tap water was better. Then I read what TDS actually measures: it isn’t a safety score, it measures dissolved substances, and some of those are useful minerals. My tests also couldn’t detect bacteria, viruses, heavy metals or other contaminants. The numbers hadn’t changed, but my interpretation had, and that question, “what if we could clean water using biology?”, led straight to my next project.

Home experiment 2 - Can bacteria and a money plant clean dirty water?

All four of Mumbai’s rivers remain in the Central Pollution Control Board’s most polluted category despite more than a decade of restoration spending, so I tested a compact bioremediation system at bench scale, which I later filed for copyright (application LD28695–2026–CO, 18/06/2026). I filled two jars with 800 mL each of dechlorinated water from the same batch of standardised synthetic wastewater, left Jar 1 untreated as the control, and gave Jar 2 a mixed bioculture, continuous aeration and a rooted money plant cutting (Epipremnum aureum). Every day I recorded how cloudy the water was and how bad it smelled on a fixed scale. The treated jar started out worse than the control, with an odour score of 5 against 4 on Day 0, but it crossed below the control between Days 2 and 3 and, by Day 6, the water had cleared and its odour had dropped to 1, while the control developed a persistent surface film and rose to 4.5. The way I read it, adding bacteria didn’t help at first, and even made things slightly worse, until the oxygen supply caught up with the oxygen demand, which may be one reason bacterial treatment has struggled in places like the Mithi River.