Water Quality for HHO Systems: Why Distilled Is the Only Option

What's in Tap Water

Municipal tap water contains chlorine, chloramines, calcium, magnesium, sodium, and dozens of other dissolved minerals. Even filtered tap water retains many of these. When you run this water through electrolysis at 8–20 amps, these minerals deposit on your electrode plates, increasing resistance, reducing active surface area, and potentially releasing chlorine gas.

Calcium Deposits Are the Main Problem

Calcium bicarbonate and magnesium in hard water deposit as calcium carbonate (limescale) on plate surfaces during electrolysis. This white coating is a resistor — it doesn't conduct electricity. Within weeks, scale-coated plates can lose 30–50% of their effective surface area and efficiency.

Chlorine Release

Chlorinated tap water produces chlorine gas at the anode during electrolysis. Chlorine is toxic and corrosive — it attacks your 316L stainless plates and can enter your engine through the gas stream. This is a safety concern beyond mere efficiency loss.

RO Water vs Distilled

Reverse osmosis (RO) water removes 90–99% of dissolved solids — much better than tap, but not as pure as distilled. RO water typically has 1–50 ppm TDS (total dissolved solids) vs near-zero for distilled. For short-term use, RO water is acceptable. For long-term operation, distilled water is the only proper choice.

How to Check Your Water

A TDS (Total Dissolved Solids) meter is a $10 investment that pays for itself. Distilled water should read under 5 ppm TDS. Tap water typically reads 100–500 ppm. Measure any water before adding it to your HHO system.