Understand How Water Purification Equipment is Tested to Ensure Quality — All in One Guide(I)

Modern consumers are increasingly concerned about drinking water quality. With countless water purifier brands on the market—ranging from basic activated carbon filters and hollow fiber membranes to UV sterilization and advanced reverse osmosis (RO) systems—there's no shortage of options. But did you know that a truly reliable water purifier must undergo a series of rigorous tests? These tests rely on a wide array of professional testing equipment.

 

Today, we’ll walk you through how water purifiers are tested, what kinds of equipment are used to verify their safety and performance, what standards these instruments must meet, and whether third-party calibration is required.

 

1. Filtration Efficiency Testing Equipment

Filtration efficiency testing is the most fundamental and critical part of the process. It can begin with simple testing instruments and progress to more advanced setups, such as quantitative dosing pumps and chemical injection devices, which provide consistent chlorine levels to verify whether filter cartridges effectively remove common contaminants.

 

Common Chemical Testing Methods Include:

(1) Dosing Pump Systems

These are used to adjust the free chlorine concentration in test water. Dosing pumps are precision devices that control the amount of chemical agents added to the water. In water purification equipment manufacturing, dosing systems typically inject sodium hypochlorite—a widely used oxidising and disinfecting agent.

 

In water treatment or purification systems, the concentration of free chlorine is a critical control parameter. It not only affects water safety but also influences the longevity of pipes and equipment. So how can we accurately control free chlorine levels and conduct effective tests? This is where dosing pumps play a vital role.

 

Chemical dosing is commonly used for:

1. Chlorination (adding sodium hypochlorite)
2. Chemical conditioning (e.g., coagulants, pH adjusters)
3. Addition of descaling agents or biocides

 

With adjustable flow rate and timing controls, dosing pumps can continuously and stably inject chemicals into the water inlet or storage tank.

Testing Purpose: To verify if the chlorine dosage is sufficient and ensure that the final free chlorine concentration in the water meets hygienic safety standards (typically between 0.2–0.8 ppm, depending on application).

 

When applying for NSF/ANSI 42 and NSF/ANSI 53 certification for activated carbon filters, water purifiers are often required to undergo testing at a high free chlorine concentration—2.0 ppm—to assess both chlorine reduction performance and contaminant removal capacity.

 

1. NSF Testing Conditions for Activated Carbon Filters (Example: Chlorine Reduction)

Key test parameters under NSF/ANSI 42 include:

• Test item: NSF/ANSI 42 requirement
• Inlet chlorine concentration: approx. 2.0 ± 0.2 ppm (mg/L) free chlorine
• Minimum reduction efficiency: ≥ 50% removal (i.e., outlet chlorine ≤ 1.0 ppm)
• Flow rate: As specified by the filter (typically 0.5–2.5 GPM)
• Total water volume (filter life): Must meet rated capacity (e.g., 750L, 1,500L, 5,000L) and maintain ≥ 50% reduction throughout
• Water pressure: Approx. 60 psi (about 4.1 kg/cm²)
• Water temperature: Approx. 20°C ± 2°C (room temperature)

 

2. How to Measure Free Chlorine Concentration in Practice

(1)Allow water to flow through the filter cartridge at a calibrated flow rate (e.g., 1 GPM).

(2)The incoming water should contain approximately 2 ppm of free chlorine.

(3)At set intervals (based on volume), take water samples and measure the free chlorine concentration in the outlet water.

(4)Continue sampling until the total filtered volume reaches the rated capacity (e.g., 1,000 gallons), and ensure the outlet chlorine concentration consistently remains ≤ 1.0 ppm (i.e., at least 50% reduction).

 

3. What Kind of Activated Carbon Filter Cartridge Can Pass the NSF-42 Chlorine Reduction Test?

Here’s an example to illustrate:

(1) An activated carbon filter cartridge is rated to treat 3,000 litres of water at a flow rate of 1 GPM.

(2) Under laboratory conditions, the inlet water contains 2.0 ppm of free chlorine. (3) If, throughout its 3,000-litre service life, the chlorine level in all sampled outlet water remains ≤ 1.0 ppm (i.e., chlorine reduction rate ≥ 50%)

(4) Then the filter cartridge can pass the NSF 42 certification for chlorine reduction.

 

Currently, Easywell Water Systems, Inc owns two dosing pump systems, which are used frequently and are maintained in excellent working condition.

 

(2) Free Chlorine Testers

A free chlorine tester is an instrument used to measure the concentration of free chlorine in water. It is commonly used in tap water, drinking water, swimming pools, industrial water treatment, or RO systems to ensure that the chlorine level is effective for disinfection without exceeding safe limits.

1. What is Free Chlorine and Why Test It?

• Free Chlorine refers to the portion of chlorine in water that has not reacted with organic matter and still retains disinfecting power.
• It is a key indicator in water treatment:
  • Too little chlorine means ineffective disinfection.
  • Too much can pose health risks and cause corrosion or irritation to equipment and users.
•  According to Taiwan’s drinking water standards, free chlorine in water should be maintained between 0.2 and 1.0 ppm (the exact limit may vary depending on the application area).

 

2. Free Chlorine Testing Procedure (Using the DPD Colorimetric Method)

(1) Collect approximately 10 mL of water sample into a test tube.

(2) Add a DPD reagent tablet or liquid.

(3) The reagent reacts with the free chlorine in the water, producing a pink colour.

(4) Use a colorimeter to measure the colour intensity, which is then converted into a ppm concentration value.

How to interpret by eye:

• The darker pink the colour, the higher the chlorine level.
• No colour (clear) indicates no free chlorine present.

Easywell Water uses a multi-parameter water quality photometer from the brand HANNA, model HI83399-01.

 

(3) Turbidity Meter

A turbidity meter is an instrument used to measure the degree of water cloudiness caused by suspended particles such as silt, organic matter, and microorganisms. It is one of the essential tools in water quality testing. This device helps determine whether water is clear or potentially contaminated.

What is Turbidity?

• Turbidity refers to the scattering of light caused by invisible impurities suspended in water.
• Higher turbidity = murkier water, which may contain substances like sediment, bacteria, organic matter, or rust particles.
• Excessive turbidity can result in:
  • Reduced effectiveness of disinfectants (e.g., free chlorine)
  • Lower overall drinking water quality
  • Faster clogging of filter cartridges and increased risk of equipment malfunction

The most common unit for turbidity is NTU (Nephelometric Turbidity Unit),

where NTU represents a standard unit for the intensity of scattered light caused by suspended particles.

(4)Taiwan Drinking Water Standards:

• The turbidity of municipal tap water at the point of distribution should be less than 1 NTU.
•  For RO (Reverse Osmosis) purified water or UF (Ultrafiltration) systems, turbidity should be below 0.1 NTU, and in many cases, it is expected to be as low as 0.01 NTU or lower.

 

(4) Conductivity Meter

A conductivity meter is an instrument used to measure the electrical conductivity of water. The higher the conductivity, the greater the amount of dissolved ions in the water—such as sodium, magnesium, nitrates, and chlorides—which indicates a higher mineral salt content. In other words, a conductivity meter is a key tool for assessing water purity, contamination levels, or mineral content.

 

(1) How is conductivity related to water quality?

Pure water itself does not conduct electricity. However, the presence of dissolved positive and negative ions enables water to conduct electricity.

Therefore:

Higher conductivity = More ions = Higher levels of minerals or pollutants in the water.

 

(2) What are the units of conductivity?

Common units of conductivity include:

• μS/cm (microsiemens per centimetre)
• mS/cm (millisiemens per centimetre) → 1 mS/cm = 1,000 μS/cm

 

Typical conductivity values:

• Ultrapure water: < 1 μS/cm
• Tap water: 200–600 μS/cm
• Seawater: approx. 50,000 μS/cm (or 50 mS/cm)

 

(3) What’s the Difference Between Conductivity (EC) and TDS?

Item	Electrical Conductivity (EC)	Total Dissolved Solids (TDS)
Unit	μS/cm	ppm
Principle	Measures conductivity (ion content)	Estimates total dissolved substances
Instrument	Conductivity Meter	TDS Meter (actually based on EC-to-TDS conversion)
Relationship		TDS ≈ EC × 0.5 ~ 0.7 (empirical factor)

Summary:

While EC directly measures the ability of water to conduct electricity (based on ion concentration), TDS is an estimate of the total amount of dissolved solids, calculated from EC using a conversion factor—typically between 0.5 and 0.7, depending on the composition of the water.

 

(5) TDS Meter (Total Dissolved Solids Tester)

A TDS meter, or Total Dissolved Solids tester, is a device used to measure the total amount of dissolved substances in water. It provides a quick and straightforward indication of how much minerals, salts, metal ions, or other soluble compounds are present in the water. TDS meters are among the most common and user-friendly tools in water quality testing.

What is TDS?

TDS (Total Dissolved Solids) refers to the total concentration of all substances dissolved in water that are not visible to the naked eye, including:

• Inorganic salts (e.g., calcium, magnesium, sodium, potassium)
•  Heavy metal ions (e.g., lead, copper, zinc)
• Organic compounds, nitrates, chlorides
• Industrial pollutants or pesticide residues

 

A TDS meter estimates the total dissolved solids in water by measuring its electrical conductivity (EC) and converting it into a TDS value. Here's how the process works:

1. The meter’s electrodes release a small electric current into the water.
2. Dissolved ions in the water conduct electricity — the higher the conductivity, the more ions are present, which means a higher TDS level.
3. The instrument then converts the conductivity reading into a TDS value, typically displayed in ppm (parts per million).

Common Reference Values for TDS Meter Readings

TDS Range (ppm)	Water Quality Interpretation
0-50 ppm	Extremely pure water (e.g., RO water, distilled water)
50-150 ppm	Low-mineral water, suitable for drinking
150-300 ppm	Typical tap water
300-500 ppm	Hard water or medium mineral content water
Over 500 ppm	High mineral content or potential contamination — not recommended for drinking

Taiwan’s Drinking Water Standard: TDS must be ≤ 1000 ppm.

(6) Microbiological Testing Systems

Microbiological testing systems are designed to analyze the presence of harmful microorganisms in water, such as bacteria, viruses, fungi, and parasites. These tests are critical for ensuring water safety, particularly in applications such as drinking water, food and beverage processing, medical-grade water systems, and swimming pools.

Below is an overview of commonly used equipment and methods for microbiological water testing:

 

1. Membrane Filtration Method + Incubator

Equipment Components:

• Membrane filtration apparatus (e.g., vacuum filter, microbial testing system)
• Sterile membrane filters with a pore size of 0.45 μm
• Selective culture media, such as EMB or m-Endo agar
• Incubator with adjustable temperature range from 35°C to 44°C
• Principle: The water sample is passed through a membrane filter, which retains bacteria on the membrane surface. The membrane is then placed on a selective culture medium and incubated for several hours up to 48 hours. The presence of microbial colonies (CFUs, Colony Forming Units) indicates contamination.

Applications：

Total Plate Count

Coliform / E. coli

Leptospira, Salmonella, and other pathogens

2. Rapid Microbial Detection Device (ATP Test)

3. Quantitative PCR Equipment (qPCR)

4. MPN，Most Probable Number

5. Microscopy and Staining Methods

 

Method	Instrument	Characteristics	Detection Time
Membrane Filtration	Membrane Filtration	Membrane Filtration	24–48 hours
ATP Test	ATP Test	ATP Test	ATP Test
PCR	qPCR Quantitative Machine	Highly sensitive, specific microbial analysis	1–3 hours
Multiple-Tube Fermentation (MPN)	MPN test tube set	Used for estimating bacterial count	24–48 hours
Microscopy	Microscope + Stains	Assists interpretation, not quantitative	Real-time observation

Currently, Easywell Water Systems, Inc. employs the membrane filtration method for microbial testing.