Feeding and water Setup and equipment
Tap water or RO water for cannabis?
Check a water report before buying filtration. EC tracks total salts, not hardness or nutrient balance. Alkalinity and individual ions help determine whether tap water, RO or a blend suits your system.
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You don’t need a filter to start. Test your water first.
Check your tap EC
| Tap EC (mS/cm) | What it means |
|---|---|
| Under about 0.1 | Low dissolved-ion content. Make sure your complete nutrient program supplies the essential minerals. |
| About 0.15 to 0.4 | Moderate. EC alone doesn’t establish suitability or identify the ions present. |
| Above about 0.5 | Find out what’s in it before deciding to treat it. EC doesn’t distinguish hardness from sodium or other salts. |
These are example EC categories, not pass/fail cutoffs for cannabis. Alkalinity, calcium, magnesium, sodium and chloride need a water report or analysis; EC and pH alone can’t identify them. High alkalinity, not high pH by itself, is a major driver of substrate pH drift.
Softened water
Use unsoftened water if you can. Sodium-exchange water softeners replace calcium and magnesium with sodium, which can build up and harm plants. Other treatment systems differ.
Chlorine and chloramine
Tap water often has small amounts of chlorine or chloramine. At drinking-water levels, they usually aren’t a problem for plants, so don’t assume ordinary tap water must be treated for every soil or microbial program. Free chlorine can dissipate if the water stands, but timing varies, and chloramine is more persistent. If a particular use does need treatment, choose a method designed for that disinfectant and follow its instructions. Don’t add an unmeasured “pinch” of chemicals.