Bangladesh Drinking Water Standards Explained: What the Numbers on Your Test Report Actually Mean

Why Understanding Standards Matters

When you receive a water quality test report, it means nothing unless you can interpret it. A TDS reading of 450 ppm — is that dangerous? An arsenic reading of 0.025 mg/L — is that within safe limits? E. coli detected at 2 CFU/100mL — is that a serious problem?

Without understanding the standards your water is being measured against, a test report gives you numbers without context. This guide provides that context — using Bangladesh's official drinking water standards (Bangladesh Standards and Testing Institution — BSTI), the World Health Organization (WHO) guidelines, and an explanation of where the two differ.

Bangladesh vs WHO Standards: Why They Are Different

Bangladesh has two sets of numbers that appear in water quality reports: Bangladesh national standards (set by BSTI) and WHO guidelines. In many cases these are the same. In some critical cases — particularly arsenic — they differ significantly.

The most important difference: Bangladesh's arsenic standard of 50 µg/L is five times higher than WHO's 10 µg/L guideline. Water that passes Bangladesh's national arsenic standard can still be above the WHO level considered safe. When evaluating your arsenic result, compare against the WHO limit of 10 µg/L — not the Bangladesh limit of 50 µg/L.

Decoding Each Parameter

TDS (Total Dissolved Solids) — mg/L or ppm

TDS is the total concentration of all dissolved substances. It does not identify which substances are dissolved — only the total load.

• Below 300 mg/L: Excellent. Refreshing taste, no scaling.
• 300–600 mg/L: Good. Acceptable taste; slight scaling on appliances.
• 600–1000 mg/L: Marginal. Noticeably hard; significant scaling risk.
• Above 1000 mg/L: Exceeds Bangladesh standard. Unpleasant taste; not suitable for drinking without treatment.

pH

pH measures acidity or alkalinity on a scale of 0–14.

• Below 6.5: Acidic — corrosive to pipes; leaches lead and copper from plumbing
• 6.5–7.5: Ideal neutral range — best taste and pipe compatibility
• 7.5–8.5: Mildly alkaline — safe; common in hard water areas
• Above 8.5: Exceeds standard — bitter taste; may indicate high carbonate minerals

Arsenic — mg/L or µg/L

Critical parameter for Bangladesh. Arsenic is naturally occurring in groundwater across large parts of the country.

• Below 0.010 mg/L (10 µg/L): Safe per WHO guideline
• 0.010–0.050 mg/L: Above WHO limit but within Bangladesh standard — still a health concern
• Above 0.050 mg/L (50 µg/L): Exceeds Bangladesh national standard — do not drink without RO treatment

Treatment: Only RO reliably removes arsenic to below both limits.

Iron — mg/L

• Below 0.1 mg/L: No visible or taste effect
• 0.1–0.3 mg/L: Borderline — may cause slight taste and staining
• Above 0.3 mg/L: Exceeds WHO aesthetic guideline — stains fixtures and laundry; damages appliances and RO membranes; requires iron removal pre-filter

Nitrate — mg/L

Note on units: Bangladesh reports nitrate as NO₃-N (nitrogen content), while some reports use NO₃ (total nitrate). The WHO limit of 50 mg/L as NO₃ is equivalent to 11.3 mg/L as NO₃-N. Confirm which units your test report uses.

• Dangerous for infants: Nitrate above 10 mg/L as NO₃-N (or 45 mg/L as NO₃) causes methemoglobinemia (blue baby syndrome) in infants under 6 months — do not use for infant formula
• Source: Usually agricultural runoff (fertiliser) or septic contamination

E. coli — CFU/100mL or MPN/100mL

E. coli is a faecal indicator organism. Any detection of E. coli in drinking water is unacceptable — there is no safe level.

• 0 CFU/100mL: Safe — no faecal contamination detected
• Any positive result: Treat as contaminated; boil or UV purify before drinking; investigate contamination source

Turbidity — NTU (Nephelometric Turbidity Units)

Turbidity measures water clarity. High turbidity indicates suspended particles that can shield microorganisms from UV treatment.

• Below 1 NTU: Excellent — effective UV treatment possible
• 1–4 NTU: Acceptable — some particle load; sediment filter recommended before UV
• Above 4 NTU: High — sediment filtration essential before any disinfection; UV will not be fully effective

Fluoride — mg/L

• Below 0.5 mg/L: Low — may be beneficial for dental health
• 0.5–1.0 mg/L: Optimal range for dental health per WHO
• Above 1.5 mg/L: Dental fluorosis risk — mottling of tooth enamel in children
• Above 4.0 mg/L: Skeletal fluorosis risk

Bangladesh's standard of 1.0 mg/L is conservative and appropriate. Most groundwater in Bangladesh is within safe limits, but elevated fluoride is documented in some areas.

Chlorine Residual — mg/L

For treated municipal supply water, some chlorine residual is desirable as it indicates ongoing disinfection protection through the distribution system.

• 0 mg/L: No residual protection — microbial recontamination risk in distribution
• 0.2–0.5 mg/L: Adequate residual — good distribution protection
• Above 1 mg/L: High — noticeable taste and odour; carbon filter recommended

How to Use Your Test Report

When you receive a water test report, work through it in this order:

1. Check E. coli first — any positive result means the water is microbiologically unsafe regardless of chemical parameters
2. Check arsenic against 10 µg/L (WHO limit) — not Bangladesh's 50 µg/L standard
3. Check TDS — above 500 mg/L means RO is warranted
4. Check iron — above 0.3 mg/L means an iron removal pre-filter is needed
5. Check nitrate — if you have an infant, any level above 10 mg/L as NO₃-N is dangerous for formula preparation
6. Check turbidity — above 4 NTU means sediment pre-filtration is essential before any purification system

Your test report is not a pass/fail document — it is a map of your specific water problems that tells you exactly which treatment technology you need.