Hydroponics tool
RO & Tap Water Mixing Calculator
Blend reverse osmosis water and tap water to estimate the right starting EC for hydroponics, indoor growing, and nutrient preparation.
Final amount of mixed water you want to prepare.
Choose liters or US gallons.
Electrical conductivity of your source tap water.
Electrical conductivity of your reverse osmosis water.
Desired EC before adding nutrients.
Recommended products for water preparation
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Final amount of water you want after mixing.
Choose liters or US gallons.
Base EC of your tap water.
Base EC of your RO water.
Desired starting EC before nutrients.
Approximate pH of your tap water.
Approximate pH of your RO water.
Tap water usually influences final pH more strongly than RO. Increase this if your tap water is highly buffered.
The pH result is an estimate only. Real mixed pH depends strongly on alkalinity, bicarbonates, dissolved minerals, and how stable your source water is. Always verify pH with a calibrated meter after mixing.
Recommended products for RO and tap water blending
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Final amount of mixed water you want to make.
Choose liters or US gallons.
Enter the tap water share of your final blend.
EC of your tap water.
EC of your RO water.
Recommended products for mixed source water
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
Water prep product
A useful product for blending water, checking EC, or stabilizing your starting solution.
RO and tap water mixing calculator for hydroponics and indoor growing
This RO and tap water mixing calculator helps growers blend reverse osmosis water and tap water to reach a target starting EC before adding nutrients. It is useful for hydroponics, coco, DWC, recirculating systems, drip irrigation, and indoor growing where source water quality affects nutrient stability and plant performance.
Use it to estimate the right blend ratio, prepare reservoir water more consistently, and reduce the guesswork when you want softer starting water than straight tap water but more mineral content than pure RO.
How this water mixing calculator works
The calculator uses weighted blending based on source water EC values. Because EC behaves approximately linearly when two water sources are mixed, the tool can estimate the tap-water fraction needed to reach a selected target EC.
What each parameter means
- Tap water EC: electrical conductivity of your tap water before nutrients.
- RO water EC: electrical conductivity of your reverse osmosis water.
- Target mixed EC: the EC you want to start with before adding feed.
- Target water volume: final total amount of mixed water.
- Tap water percentage: chosen ratio of tap water in the blend.
- Alkalinity weight: rough weighting factor showing how strongly tap water may dominate final pH.
Why growers mix RO and tap water
Pure RO water is very clean but may start too soft for some feeding strategies, while tap water may contain too much mineral content, sodium, or bicarbonate. Mixing the two gives growers more control over starting EC and often creates a more manageable base for nutrients, CalMag, and pH adjustment.
This is especially helpful when tap water is too hard for direct use but fully pure RO is not the desired starting point.
About the pH estimate
Unlike EC, pH does not mix in a simple straight-line way because alkalinity and buffering capacity matter a lot. This tool provides only a practical weighted estimate in advanced mode. Real mixed pH can differ depending on bicarbonates, dissolved minerals, and source-water chemistry.
Always measure actual pH after blending and again after adding nutrients.
Best practice for growers
- Measure both tap and RO water with a calibrated EC meter.
- Blend water first, then add nutrients.
- Check EC again after mixing to confirm the estimate.
- Adjust pH only after the final nutrient solution is complete.
- Keep notes on the blend ratios that work best for your system and source water.
Shipping. 3 day EU delivery
7 to 15 EUR under 30kg. See more on Shipping details page.
60 days returns
You can get a refund or replacement after up to 30 days from purchase.
But we ussualy stand on customers side, so we can give a 60 days time frame!
2 months post sale expert support
It's free.
We are a team of 10 with a decade of wise expirience in growing and gardening, so if you'll have any need of help, we'll guide you to your goal within 2 months from a purchase.
About us. Our 9 year history
GoToGarden started in 2017 out of personal frustration. Our founder was a hobby grower who spent hours navigating online shops that felt built by people who had never touched a plant — cluttered layouts, vague product descriptions, no real guidance on what to actually buy or why. He knew there had to be a better way.
See more on About us page
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