Methods to Reduce TDS in Water: RO vs. Distillation vs. Deionization

If your water test shows high Total Dissolved Solids (TDS), standard filters won't help. Sediment filters, carbon filters, and UV lights do not remove dissolved solids. They only remove suspended particles and bacteria.

To lower TDS, you need to physically separate the water molecule (H₂O) from the dissolved minerals. Only three major technologies can do this.

The Mechanics of Separation

How do you pull a dissolved mineral out of water? You can't filter it physically because the "holes" in a standard filter are much larger than a dissolved ion. You must use one of three physical-chemical force:

1. Reverse Osmosis (RO) — The "Sieve"

RO uses a high-pressure pump to overcomes Osmotic Pressure.

• The Membrane: A thin-film composite (TFC) with pores so small that only water molecules pass.
• The Result: It rejects 98% of minerals. It is the only way to turn seawater into drinking water economically.

2. Distillation — The "Mist"

Distillation imitates the natural rain cycle.

• The Phase Change: Water is boiled, turns into gas (leaving salts behind), and is then cooled back into liquid.
• The Purity: It is the "cleanest" method but most expensive in terms of electricity.

3. EDI (Electrodeionization) — The "Magnet"

This is the modern, high-tech standard for industrial "Ultra-Pure Water."

• The Process: It uses a combination of Ion-Exchange resins and an Electrical DC current to pull ions out of the water stream constantly.
• The Pro: Unlike standard DI filters, it never needs chemicals to regenerate. It uses electricity instead.

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Technical Comparison of TDS Removal

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When to use which?

• For your Kitchen: RO is the winner. It removes 95%+ of salt and tastes great.
• For your Car Battery: Distilled water. You don't want any conductivity.
• For Semi-conductor Labs: Two-Pass RO + EDI. This creates water so pure it doesn't even conduct electricity.

The "Low TDS" Myth: Is zero TDS bad for you?

Distilled and DI water are "hungry" water. Because they have zero minerals, they can be aggressive and slightly acidic (pH ~5.5). While drinking them won't kill you, they lack the essential Calcium and Magnesium your body needs from water. For drinking, a TDS of 100 – 300 ppm is considered the "sweet spot" for health and taste.

Comparison: Do You Need Lowest TDS?

• For Drinking: Use RO. It balances purity, cost, and practicality.
• For Car Batteries/Ironing: Use Distilled or DI water.
• For Pharmaceuticals: Use Distillation or Two-Pass RO + EDI.