Why Proper Storage Is the Final — and Often Neglected — Step
A family installs an RO+UV purifier. They test the purified water and get a clean result. They feel their water is safe. But then the purified water sits in an open container on the kitchen counter for 12 hours, is scooped out with unwashed hands multiple times, and is stored in a plastic jug that was last cleaned a month ago.
The water that enters the family's glasses may have been pure when it left the purifier. By the time it is consumed, it may be significantly recontaminated. Studies of household water quality in low- and middle-income countries consistently show that water that tests clean at the source deteriorates significantly by the time it is consumed — primarily due to unsafe storage and handling practices.
How Water Gets Recontaminated After Purification
Purified water becomes recontaminated through four main pathways:
- Hand contact — dipping unwashed hands or cups directly into a storage container introduces bacteria from skin surface
- Uncovered containers — airborne dust, insects, and splashes from nearby activities introduce contaminants
- Dirty containers — biofilm (a layer of bacteria embedded in a thin film on container walls) persists even after rinsing if containers are not properly cleaned
- Cross-contamination — using the same scooping cup for purified and unpurified water, or storing purified water near unpurified sources
The Best Containers for Storing Purified Water
Food-Grade HDPE (High-Density Polyethylene) Containers — Best All-Round Choice
Look for containers labelled "food-grade" or bearing the HDPE resin code (recycling symbol with "2" inside). These are the standard storage containers used across Bangladesh for water — the white plastic jars and pitchers widely available at every hardware store.
Advantages: Widely available, inexpensive, durable, easy to clean, lightweight
Disadvantages: Clear HDPE allows light penetration, which promotes algae growth if stored in sunlight — choose opaque white or blue containers
Sizes for household use:
- 10–20 litre covered containers with a tap — best for daily household use; tap dispenses water without hand contact
- 5 litre pitchers with lids — suitable for refrigerator storage
Stainless Steel (Food-Grade 304 or 316) — Best for Quality
Stainless steel does not leach chemicals, does not absorb odours, is easy to clean, and keeps water cooler than plastic. Higher upfront cost but lasts indefinitely.
Best for: Families concerned about microplastic contamination from plastic containers; long-term storage
Glass — Best for Taste and Purity
Glass is the safest storage material — completely inert, no chemical leaching, easy to verify cleanliness, and preserves taste perfectly.
Disadvantages: Heavy, breakable, expensive in large sizes
Best for: Small quantities (1–5 litres) stored in the refrigerator; particularly good for storing water for infant formula preparation
What to Avoid
| Container Type | Why to Avoid |
|---|---|
| Clear plastic in sunlight | Promotes algae and bacterial growth; UV degrades plastic, increasing microplastic leaching |
| Repurposed chemical containers | Impossible to fully remove chemical residue; serious contamination risk |
| Metal (non-stainless) | Iron, aluminium and copper containers corrode and leach metals into acidic purified water |
| Open containers (no lid) | Immediate recontamination risk from airborne particles, insects and hand contact |
| Earthen/clay pots (unglazed) | Porous walls allow microbial growth; difficult to clean |
How Long Does Purified Water Stay Safe?
The answer depends on storage conditions, container type and whether the water was treated with a residual disinfectant:
| Storage Condition | Safe Storage Period |
|---|---|
| Sealed, covered container, room temperature (25–35°C) | 24–48 hours |
| Sealed, covered container, refrigerated (4–8°C) | 3–5 days |
| Glass or stainless steel, sealed, refrigerated | Up to 7 days |
| Chlorinated water (residual 0.2 mg/L), covered, room temp | 3–7 days |
| RO+UV purified (no residual disinfectant), covered, room temp | 24 hours maximum |
Why RO+UV water has a shorter safe storage period: UV treatment kills microorganisms but leaves no residual disinfectant in the water. Once the water is in the storage container, it has no protection against recontamination. Chlorinated water retains a small amount of free chlorine that continues to suppress bacterial growth during storage.
For households that want longer safe storage periods, adding a small amount of food-grade chlorine (available as sodium hypochlorite solution) after purification provides residual protection — typically 2–3 drops of 5% sodium hypochlorite per litre.
The Hygiene Rules That Prevent Recontamination
These rules, applied consistently, eliminate the recontamination pathways described above:
Rule 1 — Always Use a Tap or Dedicated Ladle
Never dip hands or cups directly into a storage container. Use a container with a tap for dispensing, or a designated long-handled ladle kept clean and stored covered. The ladle/tap must never be used for unpurified water.
Rule 2 — Clean Storage Containers Weekly
Empty the container completely. Scrub the interior with a bottle brush and soap. Rinse three times with clean water. Allow to air-dry completely before refilling. Check the lid seal and tap gasket for cracks or mould.
Rule 3 — Keep Containers Covered at All Times
A loose-fitting lid is not enough — use a container with a properly sealing lid. In kitchens with cooking activity, steam and splashes from cooking can introduce contamination from distances of several metres.
Rule 4 — Store Away From Heat and Sunlight
Position storage containers in the coolest part of the kitchen, away from the stove and away from direct sunlight through windows. Every 5°C reduction in storage temperature approximately halves the rate of bacterial growth.
Rule 5 — Do Not Top Up — Empty and Refill
Do not add fresh purified water on top of existing stored water. The residual water at the bottom of an older fill may contain bacterial growth that seeds the new water immediately. Empty the container completely before refilling.
Rule 6 — Separate Containers for Different Uses
Use one dedicated container for drinking water. A separate container for cooking water. Do not interchange these with containers used for unpurified water for cleaning, bathing or washing.
Storing Water During and After Flooding
Flooding temporarily contaminates all household water sources — wells, taps and stored water. During flood conditions:
- Before flooding begins, fill all clean sealed containers with purified or boiled water. These sealed supplies remain safe during the flood.
- After flooding subsides, assume all previously stored open or unsealed water is contaminated — discard it.
- Do not use tap water or well water until the supply authority confirms restoration of safe supply and you have tested TDS and ideally bacteria.
- Use your sealed emergency supply for drinking while you purify new water.
A household that stores 20–30 litres of sealed purified water as a standard practice has a 2–4 day emergency supply available at all times — a meaningful buffer during flood events, power cuts, or supply disruptions.