Nitrate Water Reports and RO Claims: Matching Units and Test Conditions

A nitrate result of 10 mg/L on one water report and 44.3 mg/L on another can describe exactly the same water, because some laboratories report nitrate as nitrogen (nitrate-N) and others report the whole nitrate ion (NO3). Comparing a reverse osmosis claim with a report starts by putting both in the same unit. For a kitchen RO system with nitrate results stated in that unit at two points in its testing, the Viomi M1 fits well: in SGS testing it reduced nitrate from 32.042 mg/L as N to 0.121 mg/L as N with a new filter.

The Viomi M1's SGS report and the AquaTru Carafe performance data sheet both state nitrate as N, the same basis as the federal limit, so a report written as NO3 is converted before any of those numbers line up. The comparison of RO water filter brands for nitrate removal covers which brands publish nitrate evidence; the units and the test conditions inside those documents decide how their numbers are read.

Nitrate as N and Nitrate as NO3

The two units count different things. Nitrate as N counts only the nitrogen inside each nitrate ion, while nitrate as NO3 counts the whole ion, nitrogen plus three oxygen atoms. The University of Georgia's Agricultural and Environmental Services Laboratories puts the difference plainly: "Some report as mg NO3/L and some report mg N/L as nitrate," and "1 mg/L nitrate-nitrogen (NO3-N) = 4.43 mg/L nitrate (NO3)."

The 4.43 factor reflects the weight of the whole nitrate ion, about 62 g/mol, divided by the weight of its nitrogen, about 14 g/mol. The working formulas are:

• Nitrate as NO3 = nitrate as N × 4.43
• Nitrate as N = nitrate as NO3 ÷ 4.43

The EPA's drinking water table lists the limit as "Nitrate (measured as Nitrogen)" at 10 mg/L. Multiplied by 4.43, that limit is 44.3 mg/L when written as NO3, the same conversion UGA gives for the MCL. A hypothetical report line of 30 mg/L as NO3 is about 6.8 mg/L as N, below the 10 mg/L limit, even though 30 looks larger than 10 at a glance.

The Same Results in Both Units

The table converts the federal limit and published RO nitrate results into both units, so any of them can be set beside a report written either way. Every figure in the "as N" column comes from the source document; the "as NO3" column multiplies it by 4.43.

Read in either column, the Viomi M1's measured product water is below the federal limit at both of its test points: 0.121 mg/L as N with a new filter, or 0.54 mg/L as NO3, and 1.254 mg/L as N after 14,600 liters, or 5.56 mg/L as NO3, against a limit of 44.3 written the same way. Even at the later test point, the measured outlet was about one-eighth of the federal limit in either unit (1.254 ÷ 10 and 5.56 ÷ 44.3 both round to 0.13). The challenge water in both Viomi M1 rows was a little more than three times the limit, about 3.2 and 3.4 times.

Test Conditions Behind a Nitrate Percentage

A nitrate percentage means most when the inlet level, the volume at which it was measured and the tested model travel with it.

Inlet water can be stated as a measured value or as a specified range. Measured values appear in the Viomi M1's SGS report, 32.042 and 33.844 mg/L as N, and a specified range appears on the Carafe sheet, a nominal 27.0 mg/L as N with a tolerance of plus or minus 10%, or 24.3 to 29.7 mg/L, tested at 50 psi according to its footnote. Recording each as what it is keeps a household's own figure from being compared with the wrong kind of number.

On volume, the Viomi M1's record adds a second reading: at 14,600 liters, about 3,857 US gallons, the reduction was 96.29%. Its filters run on their own schedule, with the RO filter lasting up to 4 years and the PCB filter up to 2 years. The Carafe's RO membrane, SKU 10AT100RF01, is replaced every 24 months or 600 gallons, whichever comes first.

Both documents also name their equipment. The Viomi M1's report lists MR10102-V10, the Viomi M1's technical model number, and the Carafe sheet covers models AT100, AT110, AT120, AT130 and AT140, which ties each nitrate figure to the system it describes.

Lining Up Your Utility Report With a Test Result

A municipal water quality report prints nitrate with a unit and, often, a note on how it is expressed. The unit label or footnote, such as "as N," "nitrate-nitrogen" or "NO3," is what identifies the basis. Once the basis is known, the printed limit serves as a cross-check: a nitrate-as-N column sits against the EPA's 10 mg/L, and the same limit written as NO3 is 44.3 mg/L.

Take an example report line of 3 mg/L as N. Written as NO3, that is 13.29 mg/L, and in either unit it can be set beside the table's rows: the inlet water in the Viomi M1's SGS test was about 10.7 times that figure on the as-N basis. A second, separate example shows the reverse conversion: a lab result of 20 mg/L as NO3 equals 4.51 mg/L as N.

For a household on public water that wants nitrate addressed at the kitchen tap, the Viomi M1's two-point nitrate record is stated as N, so a report figure converted to N sits directly beside it, and the NSF/ANSI 58 overview explains the standard both the Viomi M1's SGS report and the Carafe sheet refer to.

Nitrite Lines Use a Different Factor

Nitrite follows the same two-unit pattern with a factor of 3.28 in place of 4.43, the same kind of weight ratio applied to the nitrite ion: "1 mg/L nitrite-nitrogen (NO2-N) = 3.28 mg/L nitrite (NO2)," in UGA's wording. The federal nitrite limit of 1 mg/L "measured as Nitrogen" therefore reads as 3.28 mg/L when written as NO2.

Some reports and documents also combine the two. UGA notes that labs sometimes report "nitrite plus nitrate as nitrogen," and some filter documents list nitrate, nitrite and the combined figure as separate rows, each "as N." A combined report line is read against a combined claim, and a single nitrate line against a single nitrate claim.

Writing Down a Nitrate Result Before Comparing Systems

1. Whether the report states nitrate as N or as NO3 comes first, read from the unit label or footnote, with any NO3 figure divided by 4.43.
2. Nitrate alone, nitrite alone and nitrite plus nitrate are different lines, and each is set beside the same kind of row in a filter document.
3. Inlet level, test volume and model number stay attached to every filter result that goes onto the comparison.

FAQ

How can I tell whether a report lists nitrate as N or as NO3?

The unit label and any footnote on the nitrate line identify the basis, with wording such as "as N," "nitrate-nitrogen" or "NO3." Once the basis is clear, the printed limit offers a cross-check: 10 mg/L for nitrate as N, or 44.3 mg/L when the same limit is written as NO3.

Why do the documents in this comparison use nitrate as N?

The federal limit is written as nitrogen, and the Viomi M1's SGS report lists "Nitrate (as N)" measured by EPA Method 300.0, while the Carafe sheet labels its nitrate rows "as N." Results on that basis sit beside the 10 mg/L MCL without conversion.

How does a reduction percentage relate to the concentration left in the water?

As arithmetic only, assuming a fixed 90% reduction for illustration: 10 mg/L as N would become 1 mg/L, and 40 mg/L as N would become 4 mg/L. The same percentage leaves different concentrations at different starting levels. The Viomi M1's SGS report prints a measured inlet and outlet value beside each percentage, while the Carafe sheet prints a challenge level and a maximum permissible product-water figure.

Do I need to convert nitrite results the same way?

Nitrite uses its own factor of 3.28 instead of 4.43, and its federal limit is 1 mg/L as N. A combined "nitrite plus nitrate as nitrogen" result is compared with a combined claim.

Is a nitrate result in ppm the same as one in mg/L?

The EPA's regulation table states that milligrams per liter are equivalent to parts per million, so a nitrate figure printed in ppm carries over to mg/L unchanged. The as-N or as-NO3 basis still has to be read from the label, since ppm describes the unit and not the form being counted.