Use this sample to understand typical inputs and the resulting index.
| Parameter | Sample Ci | Sample Si |
|---|---|---|
| pH | 7.8 | 8.5 |
| Electrical Conductivity (dS/m) | 1.5 | 3 |
| Total Dissolved Solids (mg/L) | 950 | 2000 |
| Turbidity (NTU) | 3 | 5 |
| Nitrate (mg/L) | 22 | 30 |
| Chloride (mg/L) | 130 | 140 |
| Sodium (mg/L) | 170 | 230 |
| Bicarbonate (mg/L) | 115 | 120 |
| Sodium Adsorption Ratio (SAR) | 7 | 10 |
| Residual Sodium Carbonate (meq/L) | 0.9 | 1.25 |
| Sample result | WQI 64.68 — Good | |
This calculator uses a weighted arithmetic index built from parameter sub-indices. Each selected parameter produces a sub-index Qi and a weight Wi.
- For most parameters: Qi = (Ci / Si) × 100
- For pH: Qi = |(Ci − 7) / (Si − 7)| × 100
- Auto weights: Wi = 1 / Si
- Overall index: WQI = Σ(Wi × Qi) / Σ(Wi)
- Enter your measured water values (Ci) from a lab or field test.
- Review or adjust the standard limits (Si) to match your guideline.
- Keep “Include” enabled only for parameters you measured.
- Select auto weighting for quick scoring, or choose custom weights.
- Click Calculate to see the index and category above the form.
- Use Download CSV or Download PDF to save your latest report.
Sampling and testing that fits garden irrigation
Reliable index results begin with consistent sampling. Collect water after the system runs briefly, then use clean bottles and label date, source, and weather. For wells and tanks, capture both seasonal and peak-demand periods. Field meters for pH and conductivity help with quick checks, while laboratory analysis improves accuracy for dissolved solids and ions.
Interpreting WQI for plant and soil protection
The index compresses multiple readings into one score so you can compare sources over time. Lower values indicate closer alignment with your standards. When WQI trends upward, salts, alkalinity, or sodium hazards may be increasing. Use the category message to decide whether to blend, treat, or change irrigation frequency to reduce stress on sensitive crops.
Why weights matter in real garden decisions
Auto weighting emphasizes parameters with tighter limits, which is useful when you want a conservative rating. Custom weighting is best when your garden context is known, such as high-value ornamentals or saline-tolerant groundcovers. If clogging is your priority, increase the weight for turbidity and dissolved solids so maintenance risk is reflected clearly.
Managing issues revealed by common parameters
High conductivity or dissolved solids can cause leaf burn and reduce water uptake. Elevated chloride and sodium can accumulate in root zones, especially with poor drainage. High bicarbonate may push pH upward and reduce nutrient availability. SAR and RSC relate to soil structure and infiltration; monitor them when watering clay soils or using groundwater sources.
Example data and what the score suggests
Example readings: pH 7.8, EC 1.5 dS/m, TDS 950 mg/L, Turbidity 3 NTU, Nitrate 22 mg/L, Chloride 130 mg/L, Sodium 170 mg/L, Bicarbonate 115 mg/L, SAR 7, RSC 0.9 meq/L. With the default standards and auto weighting, the sample produces a WQI of 64.68 and falls in the Good category.
Use the same set of parameters each time you test. This makes trends meaningful and helps you verify whether blending, filtration, or gypsum amendments are improving irrigation performance.
1) Which parameters should I include for a basic garden check?
Start with pH, EC, and TDS. Add sodium, chloride, bicarbonate, SAR, and turbidity when you suspect salinity, alkalinity, soil infiltration issues, or emitter clogging.
2) Can I use this index for drip systems?
Yes. Include turbidity and dissolved solids to reflect clogging risk. If you have iron or hardness data, add them by extending the parameter list and setting suitable standards.
3) Why does pH use an ideal value of seven?
The pH sub-index measures distance from neutrality because irrigation performance often worsens as water becomes strongly acidic or alkaline. You can change the standard to match your guideline.
4) What does a rising WQI over several tests mean?
A rising score indicates your water is moving farther from the selected standards. Check whether EC, sodium, bicarbonate, SAR, or turbidity is increasing and address the dominant contributor first.
5) When should I use custom weights?
Use custom weights when one risk dominates your site. For example, prioritize sodium and SAR for clay soils, or turbidity for filtration maintenance. Keep weights consistent so results remain comparable.
6) Are the default standards universal?
No. Standards vary by crop tolerance, soil type, and local guidance. Treat the defaults as a starting point, then adjust Si values to reflect your agronomy plan or laboratory recommendations.
7) How should I store results for seasonal comparison?
Calculate using the same included parameters each time, then export CSV or PDF. Track date, source, and irrigation volume so you can relate index changes to weather and management actions.