Every once in a while we get a question about a topic related to water quality, but not quite a water quality question… so today’s question came to us from ‘Michael’ who asked,

I need to purchase a quick test means to locate water leaks in supply pipes to my residential water service meter. The county water uses a small tear able foil packet of chemicals that turns red when mixed with chlorinated water. My home has very low water pressure and volume, we are serviced by an extremely old and much damaged 2″ pvc line serviced by the Logan County PSD, Logan WV. The PSD does not have the time or personnel to investigate all of the water puddles located in the community where I live. I would like to be able to quickly and safely test any ground water in the hope of finding where the line rupture is.

Thank you, Michael, for this inquiry. From the sounds of things your local water department uses DPD powder pillows or tablets to investigate the nature of puddles suspected to have formed as a result of leaks in municipal water lines. The chemical DPD turns various shades of pink through dark red in the presence of oxidizers such as chlorine, bromine, ozone, etc.

Where can the average citizen get DPD?

Chemical supply houses often carry DPD powder and/or tablets in bulk and many swimming pool stores tend to carry DPD powder pillows and tablets intended to work with swimming pool test kits.

For what you want to do, though, we suggest you look more closely at DPD powder. Specifically we think you should focus your acquisition efforts on DPD-4, a compound which will detect both free chlorine and combined chlorine in a water sample. This matters because once water treated with free chlorine exits a controlled environment (i.e. leaves the pipe through a crack, fissure, etc.) the free chlorine will immediately begin acting on any and everything in its environment… and that will result in only combined chlorine possibly reaching the surface and creating a pool of water.

Problems with testing puddles for chlorine?

While not totally impossible that a pool of chlorinated water could potentially wind up on the surface over or near a leak from a chlorinated municipal water line, we believe that only a good sized leak could produce water in the volume required to get water containing highly reactive chlorine molecules through contaminant filled soil and up to the surface — with readable/detectable chlorine residual levels high enough to detect visually (or with a portable meter) using DPD.

But, since your local water department does it, either your water line infrastructure routinely has large leaks or its water lines lie very close to the surface. Either way, a swimming pool supply company called In the Swim carries DPD-1 tablets and DPD-3 tablets.

Crushing (carefully) and then mixing them (carefully) in equal parts should enable you to create your own version of DPD-4, but to play it safe we suggest using the appropriate amount of DPD-1 in a 10 mL sample of water and then using the DPD-3 in that same sample — per the ‘accepted’ procedures for free and total chlorine concentration determination.

Today’s inquiry comes to us from a woman serving her country in the United States Navy. ‘Ronda’ had a question about the DPD products she had seen on our web site.

“Do your DPD Chlorine tabs work in Hach equipment?”

Good afternoon, Ronda, and thank you for this inquiry. When weighing the different DPD options (tablets, powders, reagentstrips, etc.) make sure you note the sample size that each test method will work in. As a general rule most devices that use DPD as a reagent will have 10 mL sample sizes, but we have also seen devices that use 15 mL sample sizes, 7 mL sample sizes and 20 mL sample sizes.

Check your machine’s manual to find out what sample size it takes. In order to remain compliant with whatever drinking water directives you follow you will need to match up the sample size w/ the correct reagent amount.

Specifically, though, you asked about the DPD tablets for chlorine testing that we have shown on our site and as far as we know all of the DPD products we have shown on our site work for 10 mL samples — except for the eXact Micro DPD products which work in smaller samples.

Two 10-mL Tablets/Strips/Powders for a 20-mL Sample?

While in theory that would work, definitely check your approved testing method to see if it expressly forbids that sort of thing and/or if it specifically calls for a brand or type of chlorine reagent delivery method. In the past we have seen where testing protocols have gotten so granular that they call out not only the type of DPD used, but also the brand of the test meter and DPD used for chlorine testing.

As we expected, the number of questions we received recently about swimming pool water has definitely increased. Today’s inquiry comes from a Water Testing Blog reader who hails from Pakistan and he/she asked:

Dear Sir/Madam,
hope you will be fine.i need some information regarding digital chlorine tester for swimming pool water .i read about extech cl200 testing metre.kindly send me the literature and price for it .
thanks
an early response is appreciable
farhan

Now before any of you go and criticize this person’s grammatical skills when typing in English, think more about the person’s commitment to keeping a proper chlorine level in swimming pool and the time it took to submit a question to this site.

WE commend ‘Farhan’ for his/her efforts and for transcending the language barrier to ask a question about proper chlorine testing in pool water.

On the topic of the “Extech 1200C” for chlorine testing in pool water, we took a look at the ExTech web site and did not find a meter in the chlorine/fluoride in water detection called the ‘Extech 1200C’… so we found ourselves a bit puzzled by your question.

We DID, however, see the ExTech CL200 Chlorine Testing Meter which uses Extech (CL203) Exstik ExTab™ Chlorine Reagent Tablets, a undoubtedly a proprietary blend of DPD-1 & DPD-3 reagents, to test for ONLY total chlorine concentrations in water.

The obvious problem we see with this meter for pool water testing, despite its USEPA credentials for total chlorine testing (in waste water), deal with the meter’s INability to test for free chlorine concentrations in water.

Proper Pool Water Testing Requires Free AND Total Chlorine Testing!

That heading said it all. Proper pool water care requires both free AND total chlorine testing.

Why? Quite simply, it does little good for the sanitation of a pool to have an in-range total chlorine reading with a very low, or non-existent, free chlorine reading. When that happens the pool contains mostly, if not entirely, chloramines (aka: combined/used chlorine molecules) which possess very little (limited) oxidizing power… and limited oxidizing power means limited sanitizing capabilities.

Improperly sanitized pool water can EASILY become a home in which various bacteria, parasites and viral ‘issues’ which will flourish, breed and infect swimmers if left unchecked.

Repeated Moral of the Story

Invest in a meter that test for both total chlorine concentrations AND free chlorine concentrations.

We suggest using a meter like the eXact Micro 7+ Pool & Spa Meter because it tests for not only free AND total chlorine, but also for Total Alkalinity, Bromine, Calcium Hardness, Copper, Ozone, Permanganate, and pH… all with the same meter!

Earlier we talked about the Extech’s USEPA credentials so naturally we figure you want to know if the eXact Micro 7+ Meter has credentials, too — and it does! When used with DPD chemistry (and the appropriate procedures, of course) the meter qualifies as an EPA Compliant device for testing free an total chlorine in drinking water.

“But Wait! There’s More!” Screamed the Announcer

As an added bonus, the eXact Micro 7+ Pool Meter also has the ability to test for Ammonia, Chloride/Salt, Chlorine Dioxide, Chromium Hexavalent, Cyanuric Acid, Iodine, Iron, Low Range Total Hardness, Manganese, Nitrate, Nitrite, Acid pH, Alkali pH, Potassium, Sulfate, Sulfide, and Turbidity — when operated in ‘% Transmission’ mode with the appropriate eXact Micro 7+ Reagent Strips.

No matter how many ‘new’ and/or ‘innovative’ methods scientists devise to make water safe for drinking, we believe a certain faction in society will still put its trust in the sanitizing effects of free chlorine. This also means we believe a need for chlorine testing will always exist.

As an immediate example of this need, a Water Testing Blog reader named John recently asked,

“Hi, I am installing a 5000 litre water tank which i intend to add chlorine to and need an inexpensive free chlorine meter could you advise me on what to purchase as this is a new venture for me. Regards, John M.”

Thank you, John, for your question. We will begin by saying that you should immediately narrow your search by eliminating any water quality testing meters not using a form of DPD-1 as the reagent for free chlorine testing.

While ORP meters do offer a good bit of utility, their readings do not directly monitor just free chlorine content of water and a great number of water quality purists still feel that traditional DPD chemistry provides the best means of determining a sample’s relative safety — based solely upon the sample’s chlorine concentration, of course.

With that said, DPD comes in several forms: Liquids, Powders, Tablets, and ReagentStrips.

To answer John’s question directly, though, at this time Water Testing Blog recommends the eXact Micro 7+ Water Testing Meter as the ‘preferred’ choice for an inexpensive meter for testing chlorine concentrations — and 20+ other water quality parameters if users desire.

Yeah, yeah, we know… we almost ALWAYS suggest the eXact Micro 7+ Meter. This time, however, since John did ask specifically about an inexpensive chlorine testing meter, the fact that Filter Water Superstore (FilterWater.Com) has the basic meter kit on sale makes it even MORE of a good choice.

Pricing verified on 2/1/2012 and the basic test kit includes…

• 1 eXact® Micro 7+ Meter
• 1 bottle of eXact® Strip Micro DPD-1 (25 tests)
• 1 bottle of eXact® Strip Micro DPD-3 (25 tests)
• 1 bottle of eXact® Strip Micro pH (25 tests)
• 1 bottle of eXact® Strip Micro Total Alkalinity (25 tests)
• 1 bottle of eXact® Strip Micro Calcium Hardness (25 tests)
• 1 bottle of eXact® Strip Micro Copper (25 tests)
• 1 Mixing Cap
• 1 Cell Cleaning Brush
• 1 Instruction Booklet
• Plastic Carrying Case
• Four AAA Batteries to power the meter

What sort of detection range does the meter have? So glad you asked!

Naturally you will want to, or you should want to, know about the cost of replacement reagent(strips) for the meter. Since John asked about chlorine testing, below you will find links to, and pricing for, replacement DPD-1 and DPD-3 ReagentStrips — currently available at several online locations such as FiltersFast.Com and FilterWater.Com.

So if you find yourself in the market for a chlorine testing meter that uses an EPA Compliant testing method AND offers additional testing capabilities, definitely take a look at the line of eXact Micro 7+ Meters.

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.

OK, so maybe not ‘new’, but having spoken with the manufacturers of this product, we can safely say that a whole lot of people who could really use this product do not know of its existence.

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?

Most people looking to test their drinking water for chlorine want to know the concentration of free chlorine, also called the free chlorine residual, in their drinking water. Basically speaking, free chlorine (hypochlorous acid) acts as an effective sanitizing and disinfecting agent in lower concentrations but can cause serious harm and damage to organic material (i.e. human skin, hair, cells, etc.) in higher concentrations.

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 on the Filters Fast web site.

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

Whether you need a basic test kit for chlorine & pH, a set of easy-to-use chlorine test strips, or an electronic chlorine testing meter, you will find the product to suit your testing needs on ChlorineTests.Com.

You can also find replacement reagents for several different chlorine test kits on ChlorineTests.Com, which naturally means you will find DPD tablets on the site for sure.

And now for a few basic chlorine testing facts:

• Test kits containing only OTO as their chlorine testing reagent will test for total chlorine only.

• Free chlorine testing requires DPD-1. Adding DPD-3 to the sample after adding DPD-1 allows a person to test for total chlorine.

• The USEPA has set the maximum contaminant level for chlorine in drinking water at 4.0ppm. This limit applies to both free chlorine levels and total chlorine levels.

• When testing for parameters other than chlorine, some test kits will require the use of chlorine eliminating agents such as sodium thiosulfate before testing can take place.

• Water containing the same amount of total chlorine as it does has very little or no free chlorine.

• The difference between the free chlorine level and the total chlorine level equals the chloramine concentration.

With so many news stories surfacing about pool water and/or drinking water not having adequate disinfectant levels many health officials have started pushing for increased testing and they don’t mean testing for chlorine residuals with test strips or liquid test kits which both require testers to match colors to get readings.

Rather than trust test personnel to use established methods of chlorine testing such as the Taylor FAS DPD Test Kit and/or the recently EPA Approved SenSafe Free Chlorine Water Check product, some folks want to remove as much subjectivity from the chlorine testing process as possible… and that means using meters to test chlorine residuals.

One example of a meter that some folks have turned to goes by the name of Extech (CL200) Exstik Direct Digital Reading Chlorine Meter and you can see a picture of that meter to the left.

The Extech CL200 Chlorine Testing Meter tests only for TOTAL chlorine, uses DPD as its reagent, requires roughly 2 minutes for testing, stores up to 15 readings internally, and detects total chlorine levels down to 0.01ppm (mg/L).

Extech, the manufacturer, claims the EPA has deemed the meter, with its associated DPD testing method, acceptable for wastewater compliance monitoring of Total Chlorine.

From what we can see on the IsoPureWater web site, this meter cannot used generic DPD tablets, DPD powder pillows, or DPD liquids designed for 10 mL sample sizes… and that means having fewer shopping options when the time comes to acquire replacement DPD reagents.

Not necessarily a show-stopper by any stretch of the imagination since a pack of 100 DPD reagent tablets for this meter costs under $30.

Definitely keep this meter in mind should you need a fast, compact meter for testing total chlorine levels in water.