# Tap water

> Tap water is municipal or well water used for irrigation; its EC, alkalinity, hardness, sodium and disinfectant vary widely, so it should be tested before use.

- Canonical: https://genetixbay.com/knowledge/glossary/tap-water.html
- Also written: mains water, municipal water, city water, faucet water, well water, hard tap water
- Glossary category: pH, EC and water · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Tap water is any drinking-quality water from a municipal supply or a private well. For growing, its relevant properties are [EC](https://genetixbay.com/knowledge/glossary/ec.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) (bicarbonate), hardness (calcium and magnesium), [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) and chloride, and the disinfectant used: [free chlorine](https://genetixbay.com/knowledge/glossary/free-chlorine.md) or chloramine. These vary by region, season and source.

## In practice

Start with the facts. Municipal suppliers publish annual water-quality reports listing hardness, alkalinity, sodium and disinfectant. Well owners should get a lab test. Then measure your own EC and pH at the tap.

Rough guide: tap EC below about 0.4 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) with moderate alkalinity (40–100 mg/L as CaCO3) is easy to use straight. EC above about 0.8 mS/cm, alkalinity above about 150 mg/L, or sodium above about 50 mg/L suggests acidifying, blending with [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), or switching to RO, especially in hydro and coco.

Hard tap water brings useful calcium and magnesium; account for it before adding [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md).

## Don't confuse with

- **RO water**: purified, near-zero EC.
- **Rainwater**: low EC and alkalinity, but can carry roof contaminants.

## Myth check

"Letting tap water stand for 24 hours makes it safe" is only partly true: it removes much free chlorine but **not chloramine**. Check your supplier's report.

## Related terms

[RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [General hardness](https://genetixbay.com/knowledge/glossary/general-hardness.md), [Chloramine](https://genetixbay.com/knowledge/glossary/chloramine.md), [Free chlorine](https://genetixbay.com/knowledge/glossary/free-chlorine.md)

## Read more

- [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md)

## Sources

1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality
2. Water Quality Association. 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf