Modern consumers are increasingly concerned about the quality of their drinking water. With a multitude of water purifier brands available on the market—ranging from basic activated carbon filters and hollow fibre membranes to UV sterilisation and advanced reverse osmosis (RO) systems—there is certainly no shortage of choice. However, did you know that a truly reliable water purifier must undergo a series of rigorous tests? These tests rely on a wide variety of specialist testing equipment.
Today, we’ll walk you through how water purifiers are tested, the types of equipment used to verify their safety and performance, the standards that apply to these instruments, and whether third-party calibration is required.
1. Filtration Efficiency Testing Equipment
Filtration efficiency testing is the most fundamental and critical stage of the process. It may begin with simple instruments and progress to more advanced systems, such as quantitative dosing pumps and chemical injection devices, which deliver consistent chlorine levels to assess 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 the test water. Dosing pumps are precision devices that regulate the amount of chemical agents introduced into the water. In the manufacture of water purification equipment, dosing systems typically inject sodium hypochlorite—a commonly used oxidising and disinfecting agent.
In water treatment or purification systems, the concentration of free chlorine is a key control parameter. It affects both water safety and the lifespan of piping and equipment. So how can we accurately control free chlorine levels and carry out effective testing? This is where dosing pumps play a vital role.
Chemical dosing is typically used for:
- Chlorination (adding sodium hypochlorite)
- Chemical conditioning (e.g., coagulants, pH adjusters)
- Addition of descaling agents or biocides
With adjustable flow rate and timing functions, dosing pumps can inject chemicals into the water inlet or storage tank in a continuous and stable manner.
Testing Purpose:
To verify whether the chlorine dosage is sufficient and ensure the final concentration of free chlorine meets hygiene and safety standards—typically between 0.2–0.8 ppm, depending on the application.
When applying for NSF/ANSI 42 and NSF/ANSI 53 certification for activated carbon filters, water purifiers are often required to be tested at high free chlorine concentrations—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 parameters for NSF/ANSI 42 testing 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 (around 4.1 kg/cm²) |
| Water temperature | approx. 20°C ± 2°C (room temperature) |
2. How to Measure Free Chlorine Concentration in Practice
- Allow water to flow through the filter cartridge at a calibrated flow rate (e.g., 1 GPM).
- The inlet water should contain approx. 2 ppm of free chlorine.
- At set intervals (based on water volume), take samples and measure the free chlorine concentration in the outlet.
- Continue sampling until the total filtered volume reaches the rated capacity (e.g., 1,000 gallons), and ensure the outlet chlorine level 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:
- A filter cartridge is rated to treat 3,000 litres of water at a flow rate of 1 GPM.
- Under lab conditions, the inlet water contains 2.0 ppm of free chlorine.
- If the chlorine level in all sampled outlet water remains ≤ 1.0 ppm during the 3,000-litre lifecycle…
- Then the filter passes NSF 42 certification for chlorine reduction.
Currently, Easywell Water Systems, Inc. owns two dosing pump systems, which are frequently used and well maintained.
(2) Free Chlorine Testers
These devices measure the concentration of free chlorine in water. Commonly used in tap water, drinking water, pools, industrial treatment, and RO systems, they ensure that chlorine levels are effective yet safe.
What is Free Chlorine and Why Measure It?
Free chlorine refers to the portion of chlorine that remains unreacted and retains disinfecting power.
- Too little: ineffective disinfection
- Too much: health risks and equipment corrosion
Taiwan’s drinking water standard:
Free chlorine should remain between 0.2–1.0 ppm (varies by region/application).
Testing Procedure (DPD Colourimetric Method):
- Collect 10 mL of water sample
- Add DPD reagent (tablet or liquid)
- The solution turns pink in proportion to chlorine content
- Measure intensity using a colorimeter (converted to ppm)
Visual Interpretation:
- Darker pink = higher chlorine
- Clear = no free chlorine present
Easywell Water uses the HANNA HI83399-01 multi-parameter photometer.
(3) Turbidity Meter
Measures water cloudiness caused by suspended particles like silt or microorganisms.
What is Turbidity?
Turbidity measures light scattering by suspended particles in water. High turbidity may indicate:
- Bacteria or rust
- Reduced disinfection effectiveness
- Faster filter clogging
- Lower drinking water quality
Unit: NTU (Nephelometric Turbidity Unit)
Standards:
- Tap water: < 1 NTU
- RO or UF systems: < 0.1 NTU (often ≤ 0.01 NTU)
(4) Conductivity Meter
Measures how well water conducts electricity—an indicator of dissolved ion levels like sodium or nitrates.
Conductivity and Water Quality:
Pure water doesn’t conduct electricity well. Ions (from salts, minerals, etc.) increase conductivity.
- Higher conductivity = more ions = greater contamination or mineral content
Units:
- μS/cm (microsiemens per cm)
- mS/cm = 1,000 μS/cm
Typical Values:
- Ultrapure water: < 1 μS/cm
- Tap water: 200–600 μS/cm
- Seawater: ~50,000 μS/cm
(5) TDS Meter (Total Dissolved Solids)
Measures the total dissolved substances (salts, metals, organics) in water, based on conductivity.
TDS Meaning:
- Inorganic salts: Ca, Mg, Na, K
- Heavy metals: Pb, Cu, Zn
- Nitrates, industrial or agricultural pollutants
Conversion:
- TDS ≈ EC × 0.5–0.7
Common TDS Ranges:
| TDS (ppm) | Water Quality |
|---|---|
| 0–50 | Ultrapure (RO, distilled) |
| 50–150 | Low mineral – drinkable |
| 150–300 | Typical tap water |
| 300–500 | High-mineral |
| >500 | Not recommended for drinking |
Taiwan Standard: TDS ≤ 1000 ppm
(6) Microbiological Testing Systems
Used to detect bacteria, viruses, fungi, and parasites—essential for water safety.
Common Equipment and Methods:
- Membrane Filtration + Incubator
- Filters retain bacteria
- Membrane placed on selective media
- Incubated at 35–44°C for up to 48 hrs
- Colony growth indicates contamination
Used for:
- Total Plate Count
- Coliforms / E. coli
- Salmonella, Leptospira, etc.
- Rapid Microbial Detection (ATP Test)
- qPCR (Quantitative Polymerase Chain Reaction)
- MPN (Most Probable Number)
- Microscopy + Staining
Comparison Table:
| Method | Instrument | Features | Detection Time |
|---|---|---|---|
| Membrane Filtration | Filtration Apparatus | Quantitative | 24–48 hrs |
| ATP Test | ATP Tester | Fast, user-friendly | Few minutes |
| PCR/qPCR | PCR Machine | Sensitive, specific | 1–3 hrs |
| MPN | Tube Sets | Estimation | 24–48 hrs |
| Microscopy | Microscope | Real-time, non-quantitative | Immediate |
Easywell Water Systems, Inc. currently uses the membrane filtration method for microbial testing.