Excellent question!
Using stored water from a sump (especially if it’s stored for several days or weeks) can lead to changes in water quality, but whether it becomes more acidic or alkaline depends on multiple factors:
🧪 1. What happens when water is stored for long periods?
| Condition | Possible Change | Cause |
|---|---|---|
| Closed sump with organic matter (leaves, algae, dust) | Becomes more acidic | Decomposition of organic matter releases acids (like humic acid) |
| Exposure to air and CO₂ | Slight acidity | CO₂ dissolves and forms carbonic acid (H₂CO₃) |
| Concrete/cement sumps | Becomes alkaline | Lime (calcium compounds) leach from walls |
| Plastic or inert tanks | Usually stable | No pH change unless contaminated |
| Stagnant water with algae | pH fluctuates | Algae can increase pH during day (photosynthesis) and drop it at night (respiration) |
⚠️ Problems of using stale sump water for irrigation:
- Acidic water (pH < 6.0) – Can cause nutrient deficiencies (calcium, magnesium) and root burn in sensitive crops.
- Alkaline water (pH > 8.0) – Reduces availability of micronutrients (iron, zinc), causes chlorosis.
- Anaerobic water – If oxygen is depleted (smelly, stagnant), harmful to soil microbes and roots.
✅ Best Practices:
- Cover your sump – Prevents algae, leaves, insects from falling in.
- Check pH periodically – Use a cheap digital pH meter (ideal irrigation water pH: 6.5–7.5).
- Clean sump every 3–6 months – Especially if algae or sludge builds up.
- Aerate the water before use if stored too long – Mix it or let it stand in open sunlight briefly.
- Avoid using water with bad smell – Indicates anaerobic bacterial growth.
🌿 Simple Tip:
Before irrigating sensitive crops like leafy greens, test a sample of sump water using:
- Litmus paper strips
- pH meter
- Or send a sample for a basic lab test if scaling up irrigation
Would you like a natural method to buffer water pH before use?