How to Test Your Home Water Quality: A Complete DIY Guide with Tools and Interpretation

Why You Should Test Your Water — Even If You Have a Purifier

A water purifier gives you the feeling of safety. A water test gives you the fact of safety. These are not the same thing. Purifier filters degrade gradually — a membrane that was removing 96% of TDS six months ago may only be removing 70% today. A UV lamp that was delivering full germicidal power when installed may have degraded to 40% output after fourteen months of continuous use.

Without testing, you cannot know whether your purifier is working. You are trusting a piece of equipment that may be silently failing. Testing takes five minutes with a basic meter and should be part of every household's monthly routine.

The Four Tests Every Household Should Do

Test 1 — TDS (Total Dissolved Solids)

Tool: Digital TDS meter (৳300–৳500)

What it measures: The total concentration of dissolved minerals, salts and metals in your water, expressed in parts per million (ppm)

How to use: Turn on the meter, dip the probe 2–3 cm into the water, wait 10 seconds for the reading to stabilise

How to interpret your results:

Test both your source water and your purified water. Calculate the rejection rate:

Rejection rate = (1 - purified TDS / source TDS) x 100

A healthy RO membrane achieves 92–97% rejection. Below 85% means the membrane needs replacement.

Important limitation: TDS measures total dissolved solids but cannot identify which solids. A TDS of 150 ppm could be predominantly safe calcium and magnesium, or it could include arsenic, lead and nitrates at dangerous levels. TDS is a screening tool — not a complete safety certificate.

Test 2 — pH

Tool: Digital pH meter (৳400–৳800) or pH test strips (৳150–৳300)

What it measures: The acidity or alkalinity of water on a scale of 0–14

Safe range for drinking water: 6.5–8.5 (WHO guideline)

How to interpret:

RO-purified water often has a slightly low pH (5.5–6.5) because the purification removes buffering minerals. If this concerns you, a mineraliser cartridge post-filter raises pH back to a neutral range.

Test 3 — Iron (Visual and Field Test)

Tool: Visual inspection + iron field test kit (৳500–৳1,200)

What it measures: Dissolved and particulate iron concentration

Visual signs of iron:

• Orange or reddish-brown colour, especially after the water has stood in a white container for 30 minutes
• Rust stains on sinks, toilets and white laundry
• Metallic taste

Iron above 0.3 mg/L (the WHO guideline) stains fixtures, damages appliances and clogs RO membranes rapidly. Field test kits use colour reagents — add drops to a water sample and match the resulting colour to a reference chart.

Test 4 — Chlorine Residual

Tool: Chlorine test strips (৳200–৳500 for a pack of 50)

What it measures: Free chlorine remaining in municipal supply water

Safe range: 0.2–0.5 mg/L (adequate disinfection); above 1 mg/L causes noticeable taste/odour

Municipal water in Bangladesh is supposed to be chlorinated. In practice, chlorine dissipates quickly — particularly during long distribution runs and hot weather. A zero chlorine reading in tap water means either the supply was not chlorinated (microbial risk) or all chlorine was consumed by high organic load in the pipes (also a risk indicator).

A carbon filter removes chlorine effectively. Test your purified water — chlorine should read zero after passing through a carbon stage.

When to Use a Laboratory Test

DIY meters and test strips handle the most common parameters. However, certain contaminants require laboratory analysis:

When to go to a lab:

• You are in or near a known arsenic-affected district
• Your TDS or pH is consistently outside the safe range despite having a purifier
• Family members have unexplained recurring health issues
• Your water source is a private well or borehole
• After any major flooding event

Laboratory options in Bangladesh:

• DPHE (Department of Public Health Engineering) offices in each district conduct basic water quality tests
• ICDDR,B and BUET Environmental Engineering labs in Dhaka
• Several private labs in Dhaka and Chittagong offer comprehensive panels

Sample collection protocol: For bacterial testing, use a sterile container provided by the lab. Run the tap for 5 minutes before collecting. Do not touch the inside of the container or cap. Deliver the sample within 6 hours and keep it cool.

Your Monthly Testing Routine

Follow this simple monthly routine to keep your household water safe:

1. Test source water TDS — note the reading
2. Test purified water TDS — calculate rejection rate
3. If rejection rate below 85% — service the RO membrane
4. Check pH of purified water — should be 6.5–8.0
5. Check chlorine in purified water — should read zero
6. Visual check of all filter housings — look for discolouration or unusual deposits
7. Log everything — date, source TDS, purified TDS, rejection rate, pH

This routine takes under ten minutes and catches problems before they affect your family's health. A simple notebook or phone note is all you need to maintain the record.