Water — Product Guide
Water purification tablets are the highest value-per-weight item in any emergency kit. A small packet of chlorine dioxide tablets addresses bacteria, viruses, and Cryptosporidium from any water source — and stores reliably for 4–5 years. The one detail that changes everything is contact time.
How it works
Water purification tablets release a chemical disinfectant into the water that kills or inactivates bacteria, protozoa, and viruses. The mechanism differs by tablet type, but the core principle is the same: the chemical must make contact with pathogens for a sufficient duration to be lethal. Contact time is the most commonly ignored specification — and the most important one.
Dropping a tablet into a water bottle and drinking after two minutes doesn't work. The contact time of 30 minutes for bacteria and viruses, and 4 hours for Cryptosporidium in cold water, is not a conservative recommendation. It's the minimum time needed for the chemistry to do its job.
The other critical variable is turbidity. Sediment and organic matter in cloudy water chemically consume the disinfectant before it can reach pathogens. Pre-filtering cloudy water through a cloth or coffee filter significantly improves treatment effectiveness. Clear water requires less chemical and less contact time than turbid water.
The contact time rule
Why contact time matters
The disinfectant must physically encounter and damage each pathogen. In the first minutes after addition, the chemical concentration is highest near the tablet and diffuses outward. After the tablet fully dissolves and the solution is stirred, the concentration equalizes throughout the water — then the clock starts for effective treatment.
Cold water extends contact time
Chemical reactions slow in cold water. The standard 30-minute contact time applies to water at 68°F (20°C) or above. In cold water (below 50°F / 10°C), double the contact time for bacteria/virus treatment. For Cryptosporidium coverage with chlorine dioxide in cold water, 4 hours is the required contact time.[1]
Pre-filter turbid water first
Always pre-filter visibly turbid water before adding tablets. Organic matter consumes the disinfectant; particles shield pathogens from contact. A coffee filter or cloth pre-filter is sufficient.
What tablets do NOT remove
Tablets treat biological threats only. For chemical contamination, use stored water. See the Water Contamination guide.
Tablet types
Chlorine dioxide, iodine, and NaDCC (sodium dichloroisocyanurate) each have different pathogen coverage, contact times, and limitations. Understanding the differences takes five minutes and changes what you put in your kit.
Katadyn Micropur MP1, Potable Aqua ClO₂
Chlorine dioxide is the current gold standard for water purification tablets. It is the only common tablet type that addresses all four major pathogen categories — including Cryptosporidium, which is resistant to standard chlorine disinfection. This makes it the appropriate choice for surface water, post-disaster conditions, and any source where Crypto is a concern.
The contact time distinction is important: 30 minutes for bacteria and viruses at room temperature, but 4 hours for Cryptosporidium at room temperature, and longer in cold water. In practice, for most domestic emergency use where the source is tap water, water from a distribution point, or a water heater, bacteria and virus coverage is sufficient — Crypto risk is lower. For surface water (streams, ponds) in any conditions, the 4-hour wait provides the full spectrum of coverage.
Taste: Chlorine dioxide is significantly better-tasting than iodine and slightly better than NaDCC. A faint chemical taste may be perceptible at the standard dose. Adding the flavoring neutralizer included in some kits masks this taste without reducing efficacy.
Shelf life note: Micropur MP1 tablets are individually foil-wrapped. Each wrapper is opened right before use — this is critical. Exposed tablets begin to degrade in hours. The 4–5 year shelf life applies to sealed individual foils.
Aquatabs, Potable Aqua (standard)
Sodium dichloroisocyanurate (NaDCC) is a chlorine-releasing compound that kills bacteria, viruses, and Giardia in 30 minutes. Aquatabs is the most widely distributed NaDCC tablet product globally — used extensively in humanitarian response. For the most common emergency water treatment scenarios in the US (tap water, municipal distribution water, water from a known clean source that needs precautionary treatment), NaDCC tablets are fast, effective, and inexpensive.
The key limitation is Cryptosporidium. NaDCC tablets are not effective against Crypto at standard dosages. For surface water, post-flood conditions, or agricultural area runoff sources, this is a meaningful gap. For most US domestic emergency scenarios involving treated municipal water that needs precautionary treatment, Crypto risk is lower — NaDCC is adequate.
Cost advantage: Aquatabs are significantly less expensive per tablet than Micropur. For a household building a large cache of backup treatment capability, NaDCC tablets provide cost-effective coverage for the most common scenarios, with a separate supply of chlorine dioxide tablets for higher-risk source water.
Taste: NaDCC water has a slight chlorine taste, less objectionable than iodine but noticeable. Vitamin C or neutralizing tablets can reduce this.
Potable Aqua iodine, Polar Pure
Iodine tablets have been used for water treatment for decades. They kill bacteria and viruses effectively, but provide only partial Giardia coverage at standard doses and no Crypto coverage. Iodine has largely been replaced by chlorine dioxide for all-around performance, but inexpensive iodine tablets remain widely available and are better than nothing.
Medical limitations: Iodine tablets are not recommended for extended use by pregnant women, people with thyroid conditions, or those with iodine allergies. Short-term emergency use is generally acceptable, but the Potable Aqua PA+ product includes a neutralizing tablet (dimethylamide) that also reduces the iodine taste. For households with thyroid concerns, chlorine dioxide or NaDCC is the appropriate choice.
Taste: The most significant limitation of iodine is taste — water treated with iodine has a strong, distinct taste that many people find unpleasant. The neutralizing PA+ tablets reduce this substantially. Vitamin C (ascorbic acid) also neutralizes residual iodine taste after treatment — add it after the full contact time, not before.
Recommendation: Iodine tablets are acceptable as a backup when chlorine dioxide or NaDCC isn't available. In a kit you're building from scratch, start with chlorine dioxide tablets instead.
Side by side
Contact times at room temperature (68°F / 20°C) for clear water. Cold water and turbid water extend required contact time. Cryptosporidium coverage requires the full 4-hour contact time for chlorine dioxide products — 30 minutes addresses bacteria and viruses only.
Tablets vs. drops
Aquamira is a two-part liquid chlorine dioxide treatment — a 1 oz bottle of Part A (chlorine dioxide solution) and a 1 oz bottle of Part B (activating agent). You mix a few drops of each in a cap, wait 5 minutes for activation, then add the activated solution to the water.
The advantage over tablets is dosage flexibility. Tablets treat a fixed volume (typically 1 liter or 1 quart per tablet). Aquamira can treat any volume precisely — 5 gallons, 10 gallons, or a bathtub full — by scaling the drop count. The two bottles together treat 60+ gallons.
The disadvantage is the activation step — you can't just drop it in the water like a tablet. In dim light or cold hands, the extra step adds friction. Tablets are faster and simpler for treating individual water bottles.
Best use case: Treating large batches of water at once — filling a 5-gallon container from a natural source, treating a full bathtub, or treating water for a family over an extended period. Tablets are better for individual bottle treatment.
Shelf life and storage
Tablets are the ideal "set and forget" emergency kit item precisely because of their shelf life. A sealed pack of Micropur MP1 tablets lasts 4–5 years without attention. Add them to every bag and forget about them until needed.
Shelf life by type
Key storage rules: keep tablets in their original sealed packaging until use, store in a cool dry location away from heat and humidity, and rotate on the printed expiration date. A tablet found loose in a bag without packaging should be considered degraded.
How many to have
Tablets are inexpensive enough to cache generously. The question is how much to keep in each location and configuration.
Personal emergency bag
A strip of 10 Micropur MP1 tablets treats 10 liters (2.6 gallons) — enough for 5 days of drinking water for one person. At under 1 oz and $5, this is the minimum every emergency bag should have.
Recommendation: 10–20 chlorine dioxide tablets per person. Supplement with a few Aquatabs for fast treatment when Crypto isn't a concern.
Family emergency supply
A family of four drinking 0.5 gallons per person per day (drinking only) for 14 days needs 28 gallons treated. At 1 tablet per liter, that's about 106 Micropur tablets — roughly 4 packs of 30.
Recommendation: 2 packs of Micropur (60 tablets) + 1 bottle of Aquamira drops (60+ gallons). Covers both individual bottle treatment and batch treatment.
Home cache
Tablets are the cheapest per-gallon backup treatment method available. A mixed cache of Aquatabs (for fast everyday treatment) and Micropur (for high-risk sources) covers all scenarios. Keep in a cool, sealed container and rotate every 4 years.
Recommendation: 100+ Aquatabs for general use, 30–60 Micropur for high-risk sources, 1 bottle Aquamira for batch treatment of large volumes.
Connected guides
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Treatment guide →
The portable filter complement to tablets — filters remove bacteria and protozoa, tablets add virus coverage. Together they cover everything.
Filter guide →
The household backup that's always available. Full EPA protocol — when bleach is appropriate and when tablets are better.
Bleach protocol →
Ready to buy?
Current pricing, specific product picks, pack size comparisons, and the cost-per-gallon analysis across all tablet types.