In the water business testing for free chlorine happens quite frequently (as Scott just said)… and we know of two ways to make that task easier:

• DPD ReagentStrips — If you use DPD-1 to test for free chlorine residual, then undoubtedly you do so using DPD in powder or tablet form. Both methods work, but DPD-1 ReagentStrips make testing for free chlorine residual in water a faster and easier process while staying in compliance with 4500-CL G. Simply insert a DPD-1 ReagentStrip into a 10mL water sample, move it back and forth (liberated required DPD chemistry off of reagent pads), and read visually or with your favorite meter.
   
• SenSafe™ Free Chlorine Water Check — In the original recommendation letter from the USEPA, dated October 2003: “We believe that the ITS test strips will provide the regulatory community with a valuable option for monitoring free chlorine levels in drinking water.” This method bears USEPA Approval for in drinking water applications.

While both testing methods make free chlorine residual testing much easier without losing accuracy, we highly suggest check with your State and Local inspectors first before using either product for compliance monitoring… because as you know (probably better than we do!), sometimes State/Local regulation changes do not always keep up with Federal Regulation changes.

‘TomToo’ very recently — as in a few minutes ago — asked about chlorine testing and which chlorine test he should use:

“Saw your chlorine sale announcement and have a question. The water in our beach house stinks really bad of chlorine when we first get there and we want to test to make sure it’s safe to use but you have free and total chlorine strips. How do you know which to use?”

Thanks for your inquiry, TomToo, and believe us when we say others share your confusion when it comes to knowing which type of chlorine they need to test for.

Lucky for you, though, we have simple answer if your concern deals only with worrying about having too much chlorine in the water. You should test for total chlorine.

The USEPA set the Maximum Contaminant Level for chlorine in drinking water at 4 ppm (parts per million) and that number takes into account ALL of the chlorine in a water sample, meaning both free and combined chlorine.

Moral of the story?

If you need to know the FULL amount of chlorine in a drinking water sample, testing for total chlorine makes the most sense.

At this time we carry 100 packs of DPD-1, DPD-3 and DPD-4 in the Water Testing Blog Test Kit Store.

Differences between DPD-1, 3 and 4?

For the answer to that question, we suggest that you take a look back at one of our earlier postings called What is DPD?. Not to brag, but we think that article does a decent job of answering the question.

To sum things up, though, below you will find the most common uses for DPD-1, DPD-3 and DPD-4:

• DPD-1 — Used by itself in a water sample to determine the free chlorine concentration in the sample.

• DPD-3 — Used after DPD-1 in a water sample to determine the sample’s total chlorine concentration.

• DPD-4 — Used by itself in a water sample to determine the total chlorine concentration in the sample.

So, before purchasing DPD, you may want to verify the type of chlorine testing that you will need to do — else run the risk of accidentally purchasing the incorrect DPD reagent(s)!

Where to purchase DPD?

As we stated earlier, you can purchase 100-packs of DPD-1, DPD-3 and DPD-4 from our Water Test Kit Store.

As for where to find other forms of DPD reagents, at this time we know of places to purchase two other forms of DPD: tablets and powder.

Need a new meter to test chlorine levels, too? We suggest looking at the eXact Chlorine Photometer available on the FilterWater.Com web site. It offers the reliability of DPD-based chlorine testing and the convenience of not having to match colors against a color chart.

Want accurate chlorine test results but don’t want to deal with DPD reagents and meters? Take a look at the SenSafe Free Chlorine water Check product currently available in our Water Test Kit Store. It bears USEPA Approval for use in municipal water testing and offers superior resistance to monochloramine interference that can sometimes affect the results obtained when testing for free chlorine residual using DPD test reagents.

Free (available) chlorine refers to the concentration of chlorine molecules residing a water sample that have not, yet, oxidized contaminants. As a general rule you want to maintain a free chlorine residual in a body of water or water source.

Therefore, if a water sample has a total chlorine residual but no free, available chlorine, then the sample may or may not be ‘safe’. Some public (municipal) drinking water systems use only combined chlorine Why would they do that?

It seems counter-intuitive that a public water systems would choose combined chlorine over free chlorine given free chlorine’s superior disinfecting (oxidizing) properties, but monochloramines do still have oxidizing capabilities and they do not create compounds (disinfection by-products, tri-halomethames, TTHM’s, etc.) that may cause cancer.

So… if you want to know how much free chlorine you have versus how much combined chlorine you have, simply subtract the free chlorine concentration from the total chlorine concentration:

(Total Chlorine) – (Free Chlorine) = Combined Chlorine

For pool water you can use a test strip like the Pool Check 6-Way to determine the free and total chlorine concentrations of a sample.

For drinking water you can use test strips like SenSafe Free Chlorine Water Check to determine the free chlorine concentration of a water sample and SenSafe Total Chlorine Water Check to determine the total chlorine concentration of a water sample.

OR, for an even easier test procedure, you can use the WaterWorks 2 Free & Total Chlorine Test Strip which tests for both free and total chlorine at the same time.

As a general rule, if your water has a chlorine smell to it, then you most likely have, at the very least, chloramines (combined chlorine) present. This does not, however, rule out the possibility that your water also may contain a free chlorine residual, too.

For the record, health officials and scientists agree that chlorine gas does NOT do the body any favors and in too great a quantity can cause lung and eye irritation… so we suggest not performing the ‘sniff test’ if you can help it.

Taste test: Not all water that contains chlorine will smell like a swimming pool. While combined chlorine (chloramines) has a strong odor associated with it, free chlorine does not. Therefore water that may not stink like chlorine may still possess a strong chlorine taste.

We do NOT advocate the taste test method for any reason. We mentioned it just so that we could talk about why water can lack a strong chlorine smell and yet still have a strong chlorine taste.

Chemical test kit: We know of many different test kits that the general public can use to determine the free and/or total chlorine concentrations in their drinking water.

“Wait… Did you just talk about two different types of chlorine?”

Yes, because as we discussed during a few moments ago, one can have free chlorine and/or combined chlorine in their water. Typically free chlorine acts as the main sanitizing and/or disinfecting agent in a chlorinated water supply and once the free chlorine finds an organic contaminant to ‘kill’, it becomes entangled with the contaminant and forms a combined chlorine molecule.

Therefore, it stands to reason that a chlorinated water supply may contain both free and combined chlorine at the same time if the free chlorine molecules have successfully neutralized all biological contaminants and the effort did not require the use/exhaustion of all free chlorine molecules present in the water supply.

Getting back to chemical test kits, please…

Now that we have established the existence of different types of chlorine which may or may not exist in a water supply, we will now discuss different ways of testing for chlorine in a water supply.

• Test Strips — Perfect for field testing because they require the user only to dip the strip into the water and compare the color of the test pad/area to a color chart that came with the package of test strips. Products exist for the detection of both free and total chlorine. People can even get a single test strip to test for both at the same using a product called WaterWorks 2
• ‘Wet’ Chemical Test Kits — Considered by most as the traditional, tried and true method for testing the quality of water. Most ‘wet’ kits typically require dissolving DPD as a tablet, powder or liquid into water samples and either comparing the colors of resultant solutions to color charts or adding drops of an additional chemical until a second color change reaction occurs.

  Simpler ‘wet chemistry’ test kits for chlorine (i.e. 2-way pool water test kits) use a different chemical called OTO (Orthotolidine) and detect total chlorine (free chlorine + combined chlorine = total chlorine).

  Problem w/ using OTO: No way exists to use OTO in a way that will allow a person to determine the free chlorine concentration.

  The DPD reagent system does, however, allow for differentiation between the two if a water sample has DPD-1 added first, gets analyzed, and then has DPD-3 added… and then get analyzed again.

• Water Testing Meters — Most water testing meters for chlorine (i.e. the eXact Chlorine Photometer) require the use of DPD, a chemical indicator which turns a shade of pink/red in the presence of chlorine molecules. DPD-1 indicates the presence of free chlorine and a combination of DPD-1 plus DPD-3 indicates the presence of free and/or combined chlorine (total chlorine).

So… Which method of chlorine testing will work best for you? Ask yourself the following questions:

1) Do you need to test for free chlorine, total chlorine or both?

2) How much accuracy and precision will you need in your results?

3) If performing testing for reporting purposes, what do the rules and regulations governing your profession say you must use as a testing methods?

Once you have answered those three questions you will have a clear idea of whether you should use chlorine test strips, wet chemistry test kits for chlorine testing or chlorine testing meters to determine chlorine concentrations in your water.

1,000 DPD #1 Tablets

Recently we received a request for a quote on 5,000 DPD #1 Tablets for chlorine (or possibly another oxidizer) level testing. We’d like to remind remind everyone that although we link to a number of water quality products, Water Testing Blog does not stock or sell any products.

The party asking about DPD #1 Tablets sought to import them into a foreign country so we suggested they contact companies on the following page:

( http://www.alibaba.com/showroom/dpd-tablets.html )

… so they could attempt to save a few bucks (or whatever currency they use) on shipping.

Now having said that, when it comes to DPD #1 we believe anyone thinking about using DPD tablets should at least consider using DPD-1 ReagentStrips in their place. ReagentStrips dissolve faster and easier than tablets (especially in hard or cold water) and contain no filler materials that could interfere with photometric optics.

As far as performance, the manufacturer of DPD-1 ReagentStrips, Industrial Test Systems, Inc., had an independent laboratory conduct a blind water sampling study using DPD ReagentStrips, Tablets and Powder Pillows. In the end the ReagentStrips tested as good, and in some cases better, than other DPD reagent delivery methods.

For years people conducting tests for certain varieties of oxidizers (Free Chlorine, Chlorine Dioxide, Bromine, Iodine, and Permanganate) have relied upon DPD-1 tablets, DPD-1 powders and DPD-1 liquids to help them obtain accurate, repeatable results.

Now, however, an easier method of adding DPD-1 reagent to test samples has become available on FilterWater.Com, an online retailer of water quality testing and water quality improvement products.

Why consider switching to DPD-1 ReagentStrips?

• The United States Environmental Protection Agency has deemed the DPD-1 ReagentStrip test procedure equivalent to USEPA method 330.5 for wastewater when used in conjunction with a Palintest Chlorometer 1000 equivalent meter (i.e. the eXact Chlorine Photometer).
• The United States Environmental Protection Agency has deemed the DPD-1 ReagentStrip test procedure equivalent to USEPA method Standard Method 4500-Cl G for drinking water when used in conjunction with a Palintest Chlorometer 1000 equivalent meter (i.e. the eXact Chlorine Photometer).
• eXact DPD-1 Reagentstrips deliver a precise dose of DPD-1 reagent into a 10 mL sample without the need to count drops (DPD-1 liquids).
• Working in the field with DPD-1 Reagentstrips becomes much easier since testing personnel will not have to worry about small or large gusts of wind blowing away their reagent as they attempt to add it to a sample (DPD-1 powders).
• Due to the ‘dehydrated nature’ of DPD-1 Reagentstrips, they will dispense rapidly and easily into hard and cold water without the need for laborious, time consuming tablet crushing (DPD-1 tablets).

• As long a the test instrument (i.e. meter or test kit) uses as standard 10 mL sample size, an eXact DPD-1 Reagentstrip will provide consistent test results regardles of who made the test kit/meter.

If you use DPD-1 on a regular basis we think you owe it to yourself to give eXact DPD-1 ReagentStrips a try.

Note: For those who know a thing or two about DPD, you may find yourself wondering why we didn’t compare the DPD-1 ReagentStrip to an old school method of reagent delivery called ampuoles which involves breaking glass tips off into test samples. Ahem… Breaking of glass in order to perform testing. Need we say anything more about ampuoles?

The US Environmental Protection Agency has set the Maximum Contaminant Level (MCL) for free chlorine at 4.0 parts per million, also known as milligrams per liter (mg/L).

The most commonly used test for free chlorine residual uses a reagent called DPD (what is DPD?). More specifically, it requires DPD-1 and DPD-1 comes in several different forms: liquid, powder, tablet and reagentstrip form.

While the average person does not have a need to for chlorine levels much above 3 to 5 parts per million, and even then they would typically only need to do so to make sure their swimming pools had a sufficient amount of free chlorine, but other folks have the need to test for free chlorine levels in excess of 25 or 50 parts per million on a regular basis. Below we will list a few of the places where you might expect to see a need for high range free chlorine testing.

Fruit & Vegetable Processing

After fresh produce leaves the fields it travels to a processing facility where it typically gets washed with a solution containing some sort of sanitizer such as chlorine, ozone, etc. In cases where the produce processing plant uses chlorine employees must make sure the rinse water contains a certain amount of free chlorine after it has passed over the fruit/vegetables.

Levels of free chlorine drop with an increase in biological load (contamination) and the rinse water having free chlorine left after use indicates that the produce no longer contains biological contamination on its surfaces.

Childcare Facilities

State laws require that childcare facilities clean their surfaces with properly mixed sanitizing and disinfecting solutions that contain an appropriate concentration of sanitizing or disinfecting chemicals. In many cases these facilities use chlorine bleach solutions for cleaning purposes.

As a general rule these solutions must contain anywhere from 50 to 200 parts per million free chlorine for sanitizing solutions and anywhere from 500 to 800 parts per million free chlorine for disinfecting solutions. In case like this the Waterworks High Range Free Chlorine Test Strips will not work because they have an upper detection limit of only 120 parts per million free chlorine, but WaterWorks Free Chlorine Check Ultra High II has an upper detection limit of 2,000 parts per million free chlorine and works well in this application.

Some states leave it up to individual childcare facilities to determine testing frequency of sanitizing and disinfecting solutions while other states, like North Carolina for example, have strict laws dictating how often childcare facilities must perform testing.

As of January 1, 2006, all licensed, non-in-home daycare centers in the State of North Carolina had to have the ability to test the chlorine bleach content in both their sanitizing and their disinfecting solutions. Previously the law stated that they had to test only the chlorine concentration in their sanitizing solutions. ( source )

If interested in purchasing a test kit for testing sanitizing & disinfecting solutions in a childcare facility, you can find them readily available in the Water Test Kit Store.

Water Lines and Water Mains

Before a water line can go into service for the first time or go back into service after a breakage or leak has gotten repaired technicians must flush (burn) the lines with water containing a high concentration of free chlorine to clean out any and biological contaminants. Typically the technicians must test the discharge water periodically until the free chlorine level remains constant at a high level for a set amount of time.

Waterworks High Range Free Chlorine Test Strips work very well for this application.

Product-specific information about Waterworks High Range Free Chlorine Test Strips:

• Testing requires just 32 seconds
• Each bottle contains 50 ready-to-use tests
• Color chart has easily distinguished color blocks at 1, 5, 10, 20, 40, 80, 120 ppm
• No harmful chemicals or reagents to handle

While many companies have moved away from single parameter water testing meters and now produce meters that can test for a number of parameters instead of just one, Hanna recently released its new Hanna Checker HC Photometer for Free Chlorine which tests exclusively for free chlorine using EPA Approved DPD-1 as its reagent.

Specifications for the Hanna Checker HC Photometer for Free Chlorine:

• Detection Range: 0.00 to 2.50 ppm (mg/L)
• Resolution: 0.01 ppm (mg/L)
• Precision: ±0.03 ppm (mg/L) @ 25°C
• Power Source: (1) 1.5 Volt AAA Battery
• Light Source: 525 nm LED
• Sample Size: 10mL
• Applicable Testing Method: Adaptation of the EPA approved DPD method Standard Method 4500-ClG

Does the Hanna Checker HC Photometer for Free Chlorine use DPD?

We already answered this one, but yes, it does. The Hanna Checker HC Photometer for Free Chlorine uses an adaptation of the EPA approved DPD method Standard Method 4500-ClG. Given that the test uses a standard 10mL sample, we would guess that the meter can use any standard DPD reagents for a 10mL sample size.

Our opinion of the meter?

• Many of us here at Water Testing Blog have large hands with clumsy fingers so meters like this one that still use cuvettes, and GLASS cuvettes at that, kind of scare us. On top of that, most pool areas prohibit the use of glass in the pool area and many food processing facilities do as well.
• The meter appears to use pouches of powder which get ripped open prior to use… and we see people accidentally spilling the DPD powder and/or having trouble pouring the powder into the little cuvette — especially if testing outdoors in a breezy climate like one might find poolside.
• Having said all that, we DO, however, think that Hanna hit a nice price point w/ this meter; not too expensive and not too inexpensive.

• Hanna MISSED the mark w/ its pricing for the DPD-1 reagents. Each test will cost nearly $0.40 to run… when other testing methods use DPD-1 reagents (i.e. DPD tablets) that cost less than $0.10 per test.