Water Sources for Greenhouse Production: Well Water, City Water & Reverse Osmosis

Why Water Quality Matters in Greenhouse Production

Water is the core of any hydroponic business. Mineral content, pH, and EC influence fertilizer programs, crop management, and final crop performance. For a broader look at how water interacts with your growing system, see our guide on hydroponics vs. aquaponics vs. aeroponics.

The Three Main Water Sources

1. Well Water

Well water is drawn from underground aquifers and is the most common in rural greenhouse operations. Its quality varies significantly by region and geology.

Typical characteristics:

• High mineral content — calcium, magnesium, iron, and bicarbonates can be an issue
• EC variable, ranging from 0.5–2.0+ mS/cm
• pH typically 7.0–8.5 — often alkaline due to dissolved carbonates
• May contain iron or manganese that can clog drip emitters

Key considerations:

• Test well water regularly through the season
• High bicarbonate levels require acid injection (phosphoric or nitric acid) to bring pH into the 5.5–6.2 target range
• Pre-existing calcium and magnesium must be factored into fertilizer formulations
• High iron levels can be an issue for drip systems and sensitive crops

2. City Water

Municipal water is treated for human consumption and is generally more consistent than well water, but has its own challenges.

Typical characteristics:

• EC typically 0.2–0.8 mS/cm — lower mineral load than most well water
• pH usually 6.5–8.0
• Contains chlorine or chloramine as disinfectants
• Sodium and fluoride may be present

Key considerations:

• Chlorine dissipates quickly with aeration or UV exposure; chloramine does not and requires activated carbon filtration or ascorbic acid treatment
• Sodium accumulation over time can raise substrate EC and cause osmotic stress — monitor regularly
• Municipal water quality reports are publicly available and provide a useful baseline, but test your own supply for accuracy
• Generally more predictable than well water, making nutrient program management easier

3. Reverse Osmosis (RO) Water

Reverse osmosis systems force water through a semi-permeable membrane, removing 95–99% of dissolved minerals, salts, and contaminants. RO water gives growers the highest level of control over their nutrient program — particularly valuable for sensitive crops like lettuce, basil, and microgreens.

Typical characteristics:

• EC near zero (0.01–0.05 mS/cm)
• pH typically 6.0–7.0 after treatment
• No chlorine or dissolved minerals

Key considerations:

• Provides maximum precision — your nutrient formula is the only source of minerals
• Ideal for sensitive crops and operations with problematic source water
• RO systems produce wastewater — typically 3–4 gallons rejected per gallon produced
• Membranes require regular maintenance and replacement
• Higher upfront cost

Quick Comparison

Factor	Well Water	City Water	Reverse Osmosis
Mineral content	High, variable	Low–moderate, consistent	Near zero
EC	0.5–2.0+ mS/cm	0.2–0.8 mS/cm	<0.05 mS/cm
pH	7.0–8.5 (often alkaline)	6.5–8.0	6.0–7.0
Consistency	Variable (seasonal)	Moderate–high	Very high
Nutrient program control	Complex — must account for existing minerals	Moderate	Maximum precision
Cost	Low (if existing well)	Low–moderate	Higher (equipment + maintenance)
Best suited for	Operations with low-mineral well water; requires testing	Most operations; watch for chloramine	Sensitive crops, high-value production, problematic source water

Further Reading

• Hydroponics vs. Aquaponics vs. Aeroponics: Which System Is Right for You?
• Controlling Tipburn in Hydroponic Lettuce (calcium & EC management)
• Microgreens for Greenhouse Production
• Good News for Greenhouse & Hydroponic Lettuce Growers

Summary

No matter your water source, the first step is to get a baseline test for pH, EC, and alkalinity. Growers using RO water have the most flexibility; those using well or city water need to account for existing minerals and pH management as part of their standard program.

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Disclaimer: Paramount Seeds is a seed supplier only. We do not sell, supply, or endorse any water treatment equipment, filtration systems, fertilizers, or nutrient products. The information in this article is for general educational purposes. Water quality varies significantly by location — always test your specific water supply and consult a qualified agronomist or irrigation specialist before making changes to your water treatment or nutrient program.