How to Read a Water Report

How to Read a Water Report

Here is the importance of understanding your water report, this applies to well water, lake water and of course city water quality report. You don’t need a science degree to understand the principles of a water report, start by narrowing it down to the main objective.

Today we’ll focus on how to read a well water analysis report. A well water report will cover 90% of what is tested in surface water samples (see Understanding Water Sources).

Water samples are typically divided into categories: organic, inorganic, microbiological and metals. There is also another list with some additional metrics or “routine water “ which include temperature, pH, turbidity, colour and ultraviolet transmission (UVT).

Standard labs will include 5-6 columns which might vary in order, they include:

  1. Parameter
  2. Unit of measure
  3. Maximum Contamination Level (MCL)
  4. Sampled result,
  5. Testing method
  6. Testing range


When choosing a water report, the lab will offer a gamma of results. A standard report will include the basics, you can add heavy metals, microbiological and organics (TOC). Some labs include bacteria counts and UVT in standard reports, make sure you ask before choosing the basics.

It’s important to know what needs to be tested, some reports for water monitoring will only need heavy metals and/or microbiological testing. Banks will often require a water report before issuing a mortgage on rural properties or a business license for commercial applications. While the bank or local health authority might only require a basic water test, as an owner, buyer or operator it’s important to include heavy metals and bacteria.

Units a measure

Since not all parameters are measured equally there are multiple units of measure. Let’s start with the most common ones:

– mg/l (milligrams per litre)
– µg/l (micrograms per litre)
– ppm (parts per million)
– ppb (parts per billion)

Without doings too much math, an easy way to remember is mg/l = ppm, and µg/l = ppb.

For easy conversion, you multiply or divide by 1000.
Example: 10 ppb /1000 = 0.010ppm

Units of measure are often missed, as reports can list parameters in ppm and then switch to ppb for heavy metals.

Other units of measure

I’ll keep this basic as you don’t want to read three pages of metric variations.

  • NTUs (Nephelometric Turbidity Units): is used to measure turbidity often attributed to sediment
  • UVT ultraviolet transmittance: this is often missed but it’s important when identifying organics and water disinfection with either UV or chlorine.
  • C/F° of course everyone is familiar with temperature units Celsius or Fahrenheit. Thankfully I haven’t seen a lab use kelvin.
  • Color units: this is primarily used to measure “color” in water which is a clear indicator of organics.
  • GPG or grains per gallon: this one is not normally displayed in your average water report, but I’ll include as it’s the unit used by water treatment professionals when treating for hardness. Total hardness in your water report will be displayed in ppm (or mg/l) when divided by 17.1 = gpg.
  • Bacteria counts: Here MPN is used as most probable number in microbiological reports, or simply bacteria reports are measured in “unit counts” or “colony counts”. This is a standard sampling technique which is often done in 10th grade science. You simply swab some sampled water on a petri dish, incubate for 24hrs, then put the dish under a microscope and count colonies or clusters. When testing water it’ll be identified as e.coli, coliform bacteria or often total bacteria.

Maximum Contamination Levels (MCL) (or MAC in Canada)

You will often see this column half blank, simply because MCL only applies to hazardous parameters including some heavy metals.

For example: arsenic (As) is a toxic metal and is clearly included with an MCL at 10 ppb (or 0.010 mg/L). While iron (Fe) is also included in the MCL columns, the number is 0.30ppm this is only to meet an aesthetic objective (AO) listed under a secondary MCL. The important difference is; primary MCL is defined by the EPA as units that must be treated to meet health guidelines, while secondary MCLs are optional, however most secondary MCLs will interfere with primary MCLs and must be pre-treated.

A common example: iron is a secondary MCL of 0.30 ppm or an aesthetic objective. Meaning iron will begin staining at 0.30 ppm, however it’s not toxic, on the other hand 20 ppb arsenic is a health hazard and should absolutely be treated, since iron interferes with arsenic filtration iron will always be pre-treated regardless of levels.

MCL guidelines

Maximum Contamination Levels were first established by the US Environmental Protection Agency (EPA) back in 1970s and have been changed or updated over the last 50 years. As science improves so does our testing techniques and long term health effects of certain contaminants. A clear example was arsenic, the EPA set a MCL level of arsenic at 50 ppb in 1996, which was then updated to the current 10ppb in 2001. As is clearly defined by both the EPA and FDA, 10 ppb arsenic is not considered a “safe level” but rather an acceptable level, these is no safe level for arsenic.

Christine Todd Whitman, the EPA administrator, stated that “the 10 ppb protects public health based on the best available science and ensures that the cost of the standard is achievable.”

Sampled column

As is obvious this is typical labeled “results”. Anything over a particular guideline either primary, secondary MCL or aesthetic objectives are typically highlighted and should include a short summary on the bottom of the report. If they are not highlighted by the lab, I encourage you to look at the MCL column and highlight everything that is over which will make it easier to review later.

Testing methods

Labs often list a code for testing methods, this might vary from lab, state or country. This isn’t always included, for regular water report reading you can ignore this column. I have only ever used this column or number when challenging a water report.

It is unusual to challenge or question a water report unless there are conflicting parameters. A common conflicting result is related to TDS (Total Dissolved Solids) for example: a hardness of 220 ppm with a TDS of 80 ppm. An easy way to understand TDS is it’s a simple addition of all dissolved minerals in water (does not include organic).

Testing range

Like testing methods this varies from lab to lab, some state labs don’t require range to be included on the main form and will have a separate sheet with ranges and testing methods. While testing ranges won’t affect your water report, understanding ranges will give you a better idea of the methods being used. Some testing methods have a specific range the better the lab the wider the range.

Example #1:

As discussed, MCL (maximum contamination levels) for iron is 0.30 ppm. Typical testing range is 0.004-25 ppm or higher.

That’s it! You can now officially read and understand a water report. Don’t let the numbered columns confuse you, they aren’t always in the same order. Before reading your water report identify the columns. I like using a highlighter to identify three factors 1) identify the top 10-12 parameters to meet potable standards (I’ll include my personal list below), 2) identify anything that is over MCL, or MAC or Aesthetic Objective (AO), 3) highlight parameters that will conflict with the above levels for treatment as explained earlier.

Example #2:

Water is considered hard over 120 ppm, but this is merely an aesthetic objective, hardness causes staining but not a health hazard, if we are using UV light for disinfection, hardness will interfere with UV disinfection by scaling the UV lamp sleeve.

Example #3:

iron MCL is 0.30ppm, but 0.20ppm while under MCL will interfere with other heavy metals specifically arsenic and uranium. It can also shorten the life of a softener. Being aware of your iron levels is important when choosing a water softener, and planning a maintenance schedule.

I hope this helps, if you have more questions feel free to use the Water Treatment Forum, we have an attach a file option where you can include your water report. We get a lot of questions that simply say “how do I treat for iron?” Because there is more than only treating iron, step number one will always be get a complete water report. We get frustrated customers that come back with “my iron is 3.2 ppm how do I treat it?”, unfortunate that is not enough. A water report will be first, then some more questions include daily volume, or how many gallons used per day and peak flow in GPM (gallons per minute). Here is another article which explains what to do after getting a water report. (link)

Final note:

If you ever get a quote or proposal from a water treatment professional which hasn’t requested a full water report, walk away! It is simply not worth the headache, we come across too many water treatment systems that were slapped together to treat for a basic water contaminant where other factors weren’t considered, you will end up throwing thousands of dollars at it trying to identify the problem without even fixing it. Here is how I compare it; imagine going to the doctor and telling them you have cancer, you then undergo 6 months of chemo and he never bothered testing what kind of cancer, tumor location or other health issues that might be affected by treatment. To all cancer patients I apologize, I do not use this in a light matter, but simply the best way to get the point across.

If you are interested in removing pollutants from water, one option is to invest in a whole house water filter which allows you to filter all incoming water to your entire property. We recently got a chance to test and recommend what we think are the best on the market.

Thanks again for reading. Feel free to add comments or questions below.