How to test the quality of distilled water?
The usual way to check how pure water is, is to measure its electrical conductivity or total dissolved solids (TDS) with a meter. NDSU Extension says pure (distilled) water is a poor conductor because it contains very few dissolved minerals, so a low reading fits distilled water. A hand meter gives only an estimate. We found no official home-test pass mark for distilled water.
Free download
Juice, Soda and Water Storage Chart (PDF): How long juice, soda, coconut water and bottled water last, opened and unopened. 19 rows, each with its source.
Thank you
Your chart is ready
We use your email only for this download.Also free:
Home Bar Storage Chart (PDF)Milk and Dairy Storage Chart (PDF)Coffee, Tea and Hot Drinks Storage Chart (PDF)Drink Strength, Calories and Units Cheat Sheet (PDF)Want the full pack? About 10 printable sheets: a larger chart for each drink type, a “has it gone off?” checklist, date labels, a party planner and an inventory sheet.
In this article
- How do you test if water is distilled?
- How do you check purity with a TDS or conductivity meter?
- What is the most exact method?
- What reading counts as pure enough?
- Should my distilled water always test 0 TDS?
- Is distilled water pH exactly 7? Why might it not test neutral (pH 7)?
- Which checks can you run on distilled water?
How do you test if water is distilled?
The FDA says water may be labeled “distilled water” if it is produced by distillation. You cannot tell by looking at it, but you can measure how many dissolved minerals (ions) it holds. NDSU Extension explains that water conducts electricity because of dissolved minerals, and that pure (distilled) water is a poor conductor because it contains very few.
How do you check purity with a TDS or conductivity meter?
- Calibrate the meter first, using the maker’s calibration solution.
- Put the probe in a clean container of the water and read the value.
- Compare the reading with a sample you know is distilled.
Meters show electrical conductivity (EC) in microsiemens per centimeter (µS/cm) or TDS in mg/L, which equals ppm. A TDS meter does not weigh minerals. It multiplies the EC reading by a conversion factor to estimate TDS, and NDSU notes the factor chart is for natural waters.
What is the most exact method?
NDSU states that the standard method for TDS is to evaporate a 0.1 liter sample and weigh the residue. A meter is a quick estimate only. If the result matters, for example for lab use, use a certified lab.
What reading counts as pure enough?
We did not find an official pass mark for home testing. The FDA rule says water called “purified water” must meet the definition in the United States Pharmacopeia; we did not read that standard. Check your device’s manual for the water type it needs.
Should my distilled water always test 0 TDS?
We found no official page that sets a required reading for home testing, so we cannot give a pass mark. What official sources do say is limited, and the rest below is our reading of it.
The USGS says that in pure water only about 1 in 55,000,000 molecules splits into hydrogen and hydroxide ions, so pure water carries almost no charge. That fits the low conductivity and low TDS expected from distilled water.
Is distilled water pH exactly 7? Why might it not test neutral (pH 7)?
The USGS also says normal rainfall has a pH of about 5.6, slightly acidic because of carbon dioxide gas from the atmosphere. The USGS page does not discuss distilled water. Our inference: if distilled water sits open to air, dissolved carbon dioxide could move its pH below 7, so a pH meter may not read exactly 7. This is not a sign of contamination by itself.
Which checks can you run on distilled water?
- Conductivity or TDS with a calibrated meter (see above), best compared with a known distilled sample.
- pH, read soon after opening the container, remembering that air exposure can shift it (our inference from the USGS rainfall note).
- For lab or medical use, a certified lab test, since the official standard method for TDS is evaporating a sample and weighing the residue (NDSU).
We found no official source describing a multimeter test for distilled water, so we do not recommend one.
People also ask
How do you test if water is distilled?
Measure its conductivity or TDS with a calibrated meter. Distilled water has very few dissolved minerals, so it conducts electricity poorly (NDSU Extension).
How do you check distilled water purity?
A calibrated conductivity or TDS meter gives a quick estimate. The standard TDS method is to evaporate a 0.1 liter sample and weigh the residue.
Is a TDS meter accurate for distilled water?
It is an estimate: it multiplies conductivity by a conversion factor that NDSU says is for natural waters. We found no official accuracy figure for distilled water.
Should my distilled water always test 0 TDS?
We found no official pass mark. Distilled water has very few dissolved minerals, so a low reading is expected, but a hand meter only gives an estimate.
Is distilled water pH exactly 7?
Not necessarily. The USGS says carbon dioxide from the air makes normal rain slightly acidic (pH about 5.6); the page does not cover distilled water, so treat a slightly lower reading as plausible, not as proof of contamination.
Why might distilled water not test exactly neutral (pH 7)?
Our inference from the USGS rainfall note: if the water sits open to air, dissolved carbon dioxide could move its pH below 7. This is not a sign of contamination by itself.
Sources
About · How we verify this · Editorial policy · Corrections
What would help you most next?
One tap. Anonymous. It helps us decide what to build.
Thank you. The free charts above are yours to keep.
