Water Analysis for Growers: How to Read EC, pH and Your Water Report

Every feeding program starts with water. Before a single fertilizer is added, your source water already contains minerals, has its own pH and its own buffering capacity. Two growers using the same nutrients can get very different results simply because their water is different. This guide explains what a water analysis tells you, how to read EC, pH and alkalinity, and how to use the report to choose and dose your base fertilizers.

Why your water analysis matters

Tap water, well water, rainwater and reverse-osmosis (RO) water can differ enormously in calcium, magnesium, sodium, bicarbonate and other elements. Whatever is already in the water becomes part of your nutrient solution. If you ignore it, you may add calcium the plant does not need, use far more acid than expected to correct the pH, or build up sodium in a recirculating system without noticing. A water analysis turns these unknowns into numbers you can work with.

What a water analysis report contains

A laboratory analysis for horticulture usually reports most of the following values:

• EC (electrical conductivity) – the total amount of dissolved salts;
• pH – how acidic or alkaline the water is at the moment of measuring;
• Alkalinity or bicarbonate (HCO₃⁻) – the buffer that resists pH changes;
• Calcium and magnesium – often present in hard water;
• Sodium and chloride – elements plants do not need in large amounts;
• Sulfate, nitrate and potassium – nutrients that may already be present;
• Trace elements such as iron, manganese, boron and zinc.

EC: the starting point of your nutrient solution

EC measures how well water conducts electricity, which rises with the amount of dissolved salts. It is usually expressed in mS/cm or µS/cm (1 mS/cm = 1,000 µS/cm). EC tells you how much is dissolved, but not what is dissolved – that is why you need the full analysis as well.

The EC of your source water is the baseline of your feed. The EC you measure in the tank is the source water EC plus everything your fertilizers add. RO water and rainwater start close to zero, which gives you full control but also means every element has to come from your nutrients. Hard tap water starts higher, so part of your EC budget is already taken before you add anything.

pH and alkalinity: two different things

pH is a snapshot: it tells you how acidic or alkaline the water is right now. Alkalinity, mostly bicarbonate, tells you how strongly the water resists a change in pH. Two waters can have the same pH but need very different amounts of acid to reach your target, because one contains much more bicarbonate than the other.

This is why the bicarbonate value on your report is so useful. It explains why the pH of some water drifts back up after correction, and it helps you predict how much acid you will need. The acid you choose also adds nutrients: phosphoric acid adds phosphorus and nitric acid adds nitrogen, so both count towards your feed. Citric acid is an option in organic programs.

Calcium and magnesium: hard water versus RO water

Hard water already supplies calcium and magnesium. If your base fertilizer does not take this into account, you may oversupply these elements. Soft water and RO water are the opposite: they contain very little calcium and magnesium, so growers usually add a calcium-magnesium supplement to fill the gap. Knowing the exact values lets you decide how much to add instead of guessing.

Sodium and chloride

Sodium and chloride are not removed by adding fertilizer – they simply add to the EC. In run-to-waste systems they leave with the drain water, but in recirculating systems they can accumulate over time. If your analysis shows high levels, blending with RO water or refreshing the solution more often are common ways to keep them under control.

Iron and other trace elements

Some waters contain iron or manganese. At higher pH these can react and become less available to the plant, or form deposits in irrigation lines. Chelated micronutrients stay available over a wider pH range, which is why professional base nutrition usually supplies trace elements in chelated form.

A practical checklist

1. Have your source water analysed by a laboratory, including EC, pH, bicarbonate, calcium, magnesium, sodium, chloride and trace elements.
2. Repeat the analysis whenever your source changes, and periodically for municipal water, which can vary through the year.
3. Measure EC and pH yourself at every mix, with meters you calibrate regularly.
4. Record the source water values next to your tank values, so you can see what your fertilizers actually add.
5. Share the analysis with your fertilizer supplier, so the base nutrition can be matched to your water.

How FertiQi uses your water analysis

FertiQi formulates base fertilizers for coco, soil and hydro to your water analysis, as liquid A+B concentrates or water-soluble powders. Send us your report together with your substrate, system and current products, and we come back with a product proposal and a feed schedule. For a complete approach to building a program, read our 6-step guide to a consistent cannabis feeding program, or see the formats and documentation we supply.

Frequently asked questions

Do I need RO water?

Not necessarily. It depends on what is in your source water. RO removes most minerals, which gives you full control, but you then have to add calcium and magnesium back. Many growers work well with tap or well water once the base nutrition is matched to it.

Is measuring EC and pH myself enough?

Daily EC and pH measurements are essential, but they do not tell you which elements are in the water. A laboratory analysis shows the composition behind the numbers, such as bicarbonate, sodium and calcium.

What EC should my nutrient solution have?

That depends on the crop, growth phase, substrate and system. Your source water EC is the starting point; the target for the tank is part of your feed schedule. Tell us about your setup and we take your water and system into account in the feed schedule we send with our proposal.

Want a base fertilizer matched to your water? Send your water analysis to info@fertiqi.com, call +34 932 53 97 24 or use the contact form.