Related guides: hydroponic nutrient-mixing guide · pH drift guide
Source water is part of every hydroponic recipe. Two growers can follow the same fertilizer label and still see different EC, pH drift, or deficiency patterns because their starting water contains different minerals and alkalinity.
Start with what you can measure
For a home system, begin with the source water you actually use. A laboratory irrigation report can include pH, EC, alkalinity, hardness, calcium, magnesium, sodium, chloride, and other elements. A handheld EC meter is useful for a baseline, but EC cannot identify which ions are present. A high reading may come from several different mineral profiles.
Alkalinity deserves special attention because it describes the water’s resistance to a pH change. High alkalinity can make pH rise repeatedly after adjustment. That is different from a single high pH reading, and the response should be based on a trend and a water report rather than repeated large doses of acid.
Use treatment for a reason
Reverse osmosis can lower the starting salt load, but it also removes calcium and magnesium that a nutrient formula may expect. If you use RO water, follow the fertilizer manufacturer’s instructions for a low-mineral base and avoid assuming that a zero EC reading means the final solution is ready.
Municipal or well water is not automatically unsuitable. For a small home garden, safe drinking water can be a reasonable starting point, but persistent symptoms, unusual EC, or a strong mineral smell justify testing. Treatment should solve a measured problem, not become a default purchase.
For the next step, see the yellow leaves troubleshooting guide.
Mix and sample consistently
- Measure the working volume rather than relying on the container’s advertised capacity. The reservoir volume calculator can help with rectangular tanks.
- Add water first, then add each nutrient part separately according to its label. Never combine concentrated parts together.
- Allow the solution to circulate, then measure EC and pH using clean, calibrated equipment.
- Record source water, product, dose, EC, pH, temperature, and the date so the next reading has context.
Connect water to symptoms carefully
Persistent upward pH, unexplained high EC, leaf-edge damage, or inconsistent crops can justify a water report. They do not identify a single nutrient deficiency on their own. Check roots, light, temperature, irrigation, and recent changes before adding supplements.
Use the PPM to EC calculator only after confirming whether a meter uses the 500 or 700 scale. For a crop reference, the hydroponic pH reference tool gives a range, not an adjustment dose.
Limitations
Water chemistry changes by location and season, and a home meter cannot replace a laboratory analysis. Nutrient formulas also differ. Use the product label, measured trends, and plant response together.
