Water purification tablets vs filter: what each does and where each one stops
Last reviewed 24 October 2026 · 7 min read
Quick checklist
Quick checklist
0 of 7 doneStart with stored tap water
In the UK, mains tap water is treated and checked before it reaches you. In an emergency, the simplest plan is to store clean tap water before you need it. Our guide to water storage containers in the UK explains how, and our guide to how much water to store for an emergency helps you work out the amount.
Treatment products come after that. They suit a short trip or a grab bag, or a back-up if your stored water runs low. They do not replace a store. If your supply stops, your water company should tell you what to do, and it can arrange alternative supplies. Our guide to what to do when the water supply is off covers what to plan.
How purification tablets and drops work
Most tablets are based on chlorine or a similar chemical. You drop one into a measured amount of water and wait for the time on the pack. Drops work in the same way, but you measure the dose yourself.
What to know:
- They need clear water. Cloudy water may need straining first. Check the instructions.
- They need time. Do not drink before the waiting time on the pack has passed.
- They taste of chemicals. Many people find the taste strong.
- They have a shelf life. Check the date, and follow the storage instructions on the pack once opened.
- They are small, light and cheap. That suits a grab bag. Water purification tablets (Retailer link coming soon) and water treatment drops (Retailer link coming soon) usually cost a few pounds, so check the current price.
Tablets and drops treat some germs, not all. They are not made to remove chemicals, fuel or heavy metals.
How a water filter works
A filter pushes or drips water through a fine membrane or cartridge that holds back particles, and, depending on the design, germs. Two types are common:
- Gravity filters sit on a worktop. You pour water in at the top and it drips through. A gravity water filter system (Retailer link coming soon) needs no power but works slowly.
- Portable filters are small, designed for outdoor trips. A portable hollow-fibre water filter (Retailer link coming soon) is light and quick to use.
What to know:
- What it treats depends on the filter. Many portable filters are rated for bacteria and protozoa but not viruses. Others add extra stages. Read the exact claims on the packaging and in the manual. Be wary of vague wording such as "makes water pure".
- The cartridge wears out. Each one has a limit on how much water it can treat. Replacement filter cartridges (Retailer link coming soon) are an extra cost, so keep a spare if you rely on one.
- It needs looking after. Follow the cleaning and storage instructions. Many makers warn that a filter that has frozen may be damaged.
Water purification tablets vs filter: a side-by-side look
| Tablets or drops | Filter | |
|---|---|---|
| What it does | Treats some germs with a chemical | Strains water through a membrane or cartridge |
| Waiting time | Yes, as stated on the pack | Depends on the design; gravity filters are slow |
| Taste | Often a chemical taste | Usually none from the filter itself |
| Weight and size | Very small | Small to bulky |
| Upkeep | Check the date; replace when used up | Clean as instructed; replace the cartridge |
| Cost | Low | Higher, plus cartridges |
| Does not remove | Chemicals, fuel, metals; may miss some parasites | Chemicals, fuel, and (for many) viruses |
| Best use | Grab bag back-up | Home or travel back-up, with a spare cartridge |
Check the exact limits for the product you choose. A table cannot replace the label.
Which should a UK household choose?
For most households with mains water, we would not buy either before water containers, a torch and some food. That is our opinion, not official advice. Once your basics are in place:
- For a grab bag, tablets are light and simple. Read the instructions before you need them.
- For home, a gravity filter is a reasonable back-up, but check what it is rated to treat and keep a spare cartridge.
- For both, treat the product as a back-up. Stored tap water stays your main supply.
Our grab bag list shows where water fits in a bag.
Where both of them stop
Neither tablets nor filters can promise safe water. In particular:
- Chemicals and fuel. Neither is designed to remove them.
- Floodwater and sewage-contaminated water. Do not drink it, treated or not. Follow your water company and local authority.
- Boil water notices. If your water company tells you to boil your water, follow its instructions. Boiling is usually what it asks for. If you cannot boil water safely, ask the company about alternative supplies. It may be able to add you to its Priority Services Register if you need extra help; see the Priority Services Register.
Do this today (free)
- Fill two clean bottles from the cold tap and label them with the date.
- Find your water company's number on a bill and save it in your phone and on paper.
- If you already own a filter or tablets, read the label and note what they are rated to treat.
If you have £10, £25 or £50
These are budgets, not quotes. Prices change, so check the current price first.
- About £10: a pack of tablets or drops for a grab bag.
- About £25: a portable filter, if you have read what it treats.
- About £50: a gravity filter, plus a spare cartridge.
Questions people ask
Are water purification tablets or a filter better?
Neither is better for every job. Tablets are small, light and cheap, so they suit a grab bag. A filter strains water without added chemicals but its cartridge wears out. Check what each product is rated to treat, follow the maker's limits and keep stored tap water as your main supply.
Do water purification tablets make any water safe to drink?
No. Tablets are designed to treat germs in clear water, within the limits on the pack. They do not remove chemicals, fuel or heavy metals, and they may not suit cloudy or contaminated water. If your water company or council says not to drink the water, follow that advice instead.
Does a water filter remove viruses?
It depends on the filter. Many portable filters are rated for bacteria and protozoa but not viruses, while others add extra stages. Read the exact claims on the packaging and the manual. If a product does not say it treats viruses, do not assume it does.
What should I do during a boil water notice?
Follow your water company's instructions exactly. They will say how to treat or replace your drinking water and for how long. Boiling is the usual method. Use a safe heat source and never a camping stove, barbecue or gas heater indoors. Ask them about alternative supplies if you cannot boil water.
Sources and further reading
Sources
firesidefolk.com/water/water-purification-tablets-vs-filter · Last reviewed 24 October 2026 · Fireside Folk