A municipal water report lists pH, hardness, alkalinity, TDS and chlorine, and this guide turns that table into a feed-water decision. Read pH off the 6.0 optimum (each unit off costs 10 points), read EC as the absolute salt load, convert hardness to ppm CaCO3 bands, run the RO arm at 95% rejection (200 ppm feed to 10 ppm permeate), size the pH buffer at |pH-6| x 1000 x 0.1 mL per 1000 L, and take RO whenever alkalinity passes 200 ppm. A worked example walks a real report line through the stacked penalties to the red or green verdict.
Key takeaways
- The Water Quality Analyzer is the feed-water screener: how to test water quality for hydroponics by reading pH off the 6.0 optimum, EC as the absolute salt reading, and hardness through the water hardness converter ppm CaCO3 bands.
- Penalties stack into a 0–100 score, the RO system calculator deri… How Water Quality Analyzer — Hardness, RO & Treatment Blueprint Helps You Master This Pick the water source type and read the feed: pH, EC, hardness in ppm CaCO3, temperature.
- Score each arm off the 6.0 pH optimum — every pH unit off costs ten, EC ten per mS, hardness one per 10 ppm, chlorine ten per ppm, metals and SAR a tail — and clamp the water quality score 0–100.
- Price the treatment: $/1000 L from the treatment base plus hardness, metals and chlorine removals, and size the pH buffer dose at |pH−6| × 1000 × 0.1 mL.
How Water Quality Analyzer — Hardness, RO & Treatment Blueprint Helps You Master This
- Pick the water source type and read the feed: pH, EC, hardness in ppm CaCO3, temperature.
- Score each arm off the 6.0 pH optimum — every pH unit off costs ten, EC ten per mS, hardness one per 10 ppm, chlorine ten per ppm, metals and SAR a tail — and clamp the water quality score 0–100.
- Classify the water: hardness bands soft/moderate/hard/very hard, TDS class off the meter scale, SAR class off the sodium hazard.
- Run the RO system arm: permeate = feed TDS × (1 − rejection/100), read against the 95% membrane guideline.
- Price the treatment: $/1000 L from the treatment base plus hardness, metals and chlorine removals, and size the pH buffer dose at |pH−6| × 1000 × 0.1 mL.
- Read the band — green above 80, yellow 60–80, red under 60 or metals over 50 ppb or effective chlorine over 2 ppm — and honor the >200 ppm alkalinity "RO Recommended" flag.
The Formula Behind the Result
Water quality score — stacked penalties off the 6.0 optimum → Q = 100 - left(10,|pH - 6.0| + 10,EC + 0.1,H + 10,Cl_{eff} + 0.001,M + 5,SARright), quad 0 le Q le 100Effective chlorine — residual after the treatment in line → Cl_{eff} = Cl cdot f(t), qquad f(text{carbon}) = 0.05, f(text{RO}) = 0.02, f(text{UV}) = 0.8, f(text{none}/text{softener}) = 1.0Hardness classification — ppm CaCO3 bands → text{Soft} le 60 < text{Moderate} le 120 < text{Hard} le 180 < text{Very hard}, quad 1,text{gpg} approx 17.1,text{ppm CaCO}_3RO permeate — membrane rejection on the feed TDS → P_{permeate} = TDS cdot left(1 - frac{r}{100}right), qquad r = 95%: 200 rightarrow 10,text{ppm}Treatment cost — base plus what the water forces you to remove → C = C_{base} + 0.01,H + 0.001,M + 0.1,Cl quad ($ / 1000,text{L})pH buffer — acid-equivalent dose off the optimum → B = |pH - 6.0| cdot 1000 cdot 0.1 quad (text{mL} text{per} 1000,text{L})TDS from EC — scale must be stated, EC is the absolute → TDS_{500} = EC times 500,qquad TDS_{700} = EC times 700 quad (text{meter-scale dependent})Safety bands — the bound the whole screener lives in → text{Green: } Q > 80,quad text{Yellow: } 60 le Q le 80,quad text{Red: } Q < 60 text{or} M > 50 text{or} Cl_{eff} > 2
Target Ranges: What the Numbers Should Be
- pH 6.0 is the nutrient-availability optimum: the archived pH-adjuster drove from the same 5.5–6.5 band, and pH is logarithmic so 5.0 is ten-times more acidic than 6.0.
- Hardness in ppm CaCO3 doubles as carbonate alkalinity that fights your pH; 1 gpg ≈ 17.1 ppm and 1 dH ≈ 17.9 ppm for the water hardness converter.
- RO at the archived 95% rejection turns a 200 ppm feed into a 10 ppm permeate; a 4-stage membrane strips salts and metals together, and the archived pH-adjuster called for RO once alkalinity passed 200 ppm.
- Treatment cost scales with what the water forces you to remove: +$0.01 per hardness ppm, +$0.001 per lead/copper ppb, +$0.10 per chlorine ppm on the $/1000 L reference.
- Carbon and RO leave only a 2–5% chlorine residual while UV alone leaves 80% — effective chlorine is what actually reaches the roots, and >2 ppm reads red.
Use the free Yield & Economics Calculator — Harvest, Dry Weight & ROI Blueprint to run the numbers on your own setup.
Use the free Climate Controller & HVAC Sizer — VPD, Dehumidifier & CO2 Blueprint to run the numbers on your own setup.
Use the free Nutrient Antagonism Lockout Predictor Mulder Matrix Solver to run the numbers on your own setup.
Compare every free calculator side-by-side on the MistCulture tools hub — each one keeps your workspace in sync.
Related guides
Reading a real report: the pH 7.8, 0.6 mS line
Report line: pH 7.8, hardness 150 ppm CaCO3, alkalinity 210 ppm, EC 0.6 mS/cm, chlorine 1.2 ppm, metals under 50 ppb. Each value is scored on its own arm, then the penalties are stacked off the 100 base.
- pH penalty: |7.8 – 6.0| = 1.8 units x 10 = 18 points.
- Hardness: 150 ppm CaCO3 lands in the Hard band (120-180) and scores 15 points (1 point per 10 ppm).
- EC 0.6 mS/cm scores 6 points; chlorine 1.2 ppm scores 12 points; metals add 0.
- Total Q = 100 – (18 + 15 + 6 + 12) = 49, which reads red on the safety bands (under 60).
- Alkalinity passes the 200 ppm threshold, so the screener flags RO Recommended before treatment is priced.
- RO line: 95% rejection turns a 200 ppm feed into a 10 ppm permeate (200 x 0.05); a 4-stage membrane strips salts and metals together.
- pH buffer dose: |7.8 – 6.0| x 1000 x 0.1 = 180 mL of acid equivalent per 1000 L of feed.
- Treatment cost: base + 0.01 x 150 (hardness) + 0.10 x 1.2 (chlorine) per 1000 L, before choosing RO over carbon.
Frequently Asked Questions
References & Science
- Cornell CALS — hydroponic research manual
- NCSU CALS — Vapor Pressure Deficit resources
- Purdue Extension — hydroponics guide
Frequently asked questions
How do I read a tap water report?
Find the columns for pH, hardness and alkalinity in ppm CaCO3, TDS or EC (note the meter scale), and residual chlorine. Score each arm off the 6.0 pH optimum: every pH unit costs 10 points, EC 10 per mS, hardness 1 per 10 ppm, chlorine 10 per ppm. When alkalinity exceeds 200 ppm, plan on RO with a 95% rejection membrane rather than acid alone.
What is the most common reading mistake?
Trusting the printed report instead of measuring the actual tap. The report is an annual average, not the water on delivery day: chlorine decays, hardness shifts seasonally, and the pH can drift in the pipes. Re-test pH, EC and alkalinity, state the TDS scale on your meter, and treat the printed values as the starting point for the |pH-6| x 1000 x 0.1 mL buffer dose.
Which calculators should my report numbers go through?
The Water Quality Analyzer embedded on this page scores the full feed on the stacked penalties, sizes the RO arm against the 95% membrane guideline, and returns the pH buffer dose. The Nutrient Antagonism Lockout Predictor and Nutrient Lab Pro handle the ion ratios that follow, and the tools hub keeps the workspace in sync.
References
- Hoagland, D. R. & Arnon, D. I. (1950) — The Water-Culture Method for Growing Plants Without Soil
- Sonnenveld, C. & Voogt, W. — Plant Nutrition of Greenhouse Crops, Springer
- Resh, H. M. — Hydroponic Food Production (7th ed.), CRC Press
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