Katadyn Micropur Classic: Keeping Stored Tap Water Fresh

Katadyn Micropur Classic is a silver-based water preservative, not a purifier. Its job is to keep tap water that is already fit to drink fresh inside a clean container, so that a household store is still pleasant and free from germs weeks later. The maker states that silver ions preserve water for up to 6 months¹, and that the water needs 120 minutes of contact time before it is protected².

That combination, a long preservation period and a two hour wait at the start, is what shapes how you use it. You fill a clean container with clear tap water, dose it at the rate for your format, wait 120 minutes, and then the water is protected for up to 6 months². It keeps water free from germs, algae and odours and protects it from bacterial recontamination⁴.

It comes in four formats: two tablet tubs, a liquid and two powder packs, each aimed at a different size of container and household. This page sets out what each one does, the dose and contact time, why the water must be clear, which containers are suitable, how long the product keeps in storage, and how to handle it safely. If you are still deciding how much water to keep in the first place, start with how much drinking water to store per person.

What Micropur Classic does, and what it does not

The active ingredient is silver. Katadyn states that the effect is based on the bacteriostatic and bactericidal properties of silver, and that silver ions cling to the cell walls of microorganisms, hindering their growth⁹. In practice that means the product holds a body of clean water in good condition rather than rescuing a dirty one.

The maker's own description is that Micropur Classic inactivates bacteria in water tanks and containers and keeps water free from germs, algae and odours¹⁰. It also protects water from bacterial recontamination⁴, which matters in a container you open repeatedly over weeks. Katadyn notes it can be used wherever drinking water remains in a system for a long time².

The distinction that matters most for a household is between preserving and purifying. Every format lists its water source as tap water¹¹. If your supply is off, unsafe or under a do not drink notice, the first job is to get safe water, not to preserve doubtful water. Our guide to how to make water safe to drink in an emergency covers the methods for that, and do not drink and do not use notices explains what a notice means for your taps.

Once you have safe water, Micropur Classic is what lets you store it in bulk without it turning. That is the gap it fills: a container of tap water left standing for a fortnight is not something most households would want to drink, and a treated one is protected for up to 6 months¹.

The four formats and the volumes each one suits

The range splits by container size and by how many people you are supplying. The tablets suit bottles and small containers, the liquid suits mid-sized tanks and travel, and the powders suit large static tanks.

The pattern is straightforward. The MC 1T tablet is the bottle and small jerrycan format, one tablet to the litre. The MC 10T is the larger container format, one tablet to 10 litres, which suits a 10 to 50 litre jerrycan or a small tank⁴. The liquid is the travel and mid-size tank option, dosed by millilitre, and the two powders are for static tanks measured in hundreds or thousands of litres¹².

For a household working out what to buy, the tablet tubs are the simplest to use because the dose is a whole tablet. The powders need a measure, which is fine for a tank you dose once and leave. If you are choosing between this and other approaches, our comparison of purification tablets: chlorine, chlorine dioxide and silver sets the chemistries side by side.

Dosage and contact time: 120 minutes before the water is protected

Every format in the range carries the same exposure time: 120 minutes². That is the period between dosing and the water being protected, and it is the figure people most often get wrong by treating the water as ready the moment the tablet goes in.

The steps are the same whatever the format:

1. Start with clear tap water in a clean container.
2. Add the dose for that format and that volume: one tablet per litre for the MC 1T², one tablet per 10 litres for the MC 10T⁴, 1 ml per 10 l for the liquid⁷, or 1 g per 100 l for the MC 10.000P powder¹².
3. Wait 120 minutes before the water is protected².
4. Keep the container closed and use the water within the preservation period of up to 6 months¹.

The dose scales with the format, not with the container's nominal size. A jerrycan dosed with the MC 10T needs the dose for the volume of water it actually holds, not a single tablet for a 1 litre container.

Clear water only: why cloudy water weakens the silver

The maker is explicit that this is a product for clear water. Katadyn states that it is for clear, not for cloudy water, as suspended matter will weaken the effect of silver ions⁴. The same instruction appears across the range¹.

The reason is mechanical. Silver ions work by reaching the cell walls of microorganisms⁹. Suspended particles in cloudy water give those organisms somewhere to sit and give the silver something else to cling to, so the effect is weakened. Cloudy water is also a sign that something is in the water that you would rather not be storing for months.

If your tap water runs cloudy, let it settle and clear before you treat it, and check whether the cloudiness is the harmless milky appearance caused by air in the supply. Our page on why tap water is cloudy or milky explains the difference. If the water is discoloured rather than merely aerated, brown or discoloured tap water covers what to do and how long it takes to clear.

The same rule applies to water you have collected yourself. Micropur Classic is not the tool for a stream or a rainwater butt, because that water is neither clear nor known to be safe. Our guide to drinking from streams, rivers and other sources safely covers what to do with collected water before it goes anywhere near a storage container.

Containers it can go in, and the metal check to do first

The maker's container advice is consistent across every format: it can be used in plastic or glass, and metals should be checked before use⁷. The powder pages add the same point in a different form, advising use in clear water and a check of metal compatibility first¹².

That gives a simple rule for a household store. Plastic jerrycans, plastic bottles, glass demijohns and plastic water tanks are all in scope. Metal containers, metal taps, metal tank fittings and metal pipework need checking with the container or tank supplier before you dose, because the maker does not state that they are suitable without that check.

For the containers themselves, our guide to containers and jerrycans for drinking supplies covers what to look for, and household storage tanks for drinking supplies covers the larger fixed options. Whichever you use, clean it before filling: a container that has held something else, or has been standing open in a garage, is not a good home for six months of drinking water.

Shelf life: 10 years for tablets and powder, 5 for the liquid

Storage life is one of the practical reasons this range suits a household store. The tablets and both powders carry a shelf life of 10 years². The liquid carries a shelf life of 5 years⁷.

That difference is worth planning around. A tub of tablets bought and put in a cupboard will still be in date a decade later, which makes it easy to keep a reserve and forget about it. The liquid needs a date on the bottle and a reminder to replace it sooner. Our page on how long purification tablets last goes into the general question.

A product past its shelf life is not something to build a water plan on.

Handling, hazard warnings and disposal

Every format in the range carries the signal word Warning⁷. The maker's safety instruction is the same on each: use biocides safely, always read the label and product information before use⁷.

The hazard statement on the packs is H410, very toxic to aquatic life with long lasting effects⁷. That is a warning about what the product does if it reaches a pond, a stream or a drain, not a warning about drinking correctly dosed water. It does mean you should not tip leftover liquid, powder or old treated water into a watercourse.

Disposal is by local rules. Katadyn's instruction is to dispose of contents and container in accordance with local legislation¹², which in the UK means your council's arrangements for household chemical waste rather than the ordinary bin where your council says otherwise.

Registration, item numbers and buying the right format

Each format carries a German biocide registration number, which is a useful identity check when you are buying. The MC 1T tablets are registered as Baua Reg. Nr. N-58034², the MC 1'000F liquid as N-58032⁷, and the MC 10.000P and MC 50'000P powders as N-58033¹². Each is described as a regulated biocide under PT 5⁷.

The item numbers and barcodes let you confirm which pack you have:

The range is made by Katadyn, and the maker's own pages are the place to confirm a specification before you buy. Where a retailer lists a different figure from the maker, take the maker's figure.

Using it in a caravan, boat or static tank

The powder formats are the ones aimed at tanks. Katadyn describes the MC 10.000P as ideal for conserving water in boats, campers, caravans, huts, in water tanks and containers and more¹². It is dosed at 1 g per 100 l and suits tanks from 100 L to 10,000 L¹².

For a caravan or boat, that means you can dose the onboard tank at the start of a season and have protected water for up to 6 months¹². The same conditions apply as anywhere else: the tank needs to hold clear water, and any metal fittings need checking with the maker of the tank before you dose¹². A tank that has stood with old water in it should be cleaned and refilled before treatment, not dosed on top of whatever is already there.

The MC 50'000P is the larger version of the same idea, for groups of more than 10 people and volumes up to 50'000 L¹³. For a household with a fixed storage tank, our guide to household storage tanks for drinking supplies covers the tank side of the job.