Can cats drink tap water, or is filtered or bottled better?
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Can cats drink tap water? In France, tap water is suitable in virtually every municipality: it’s drinkable, subject to regular health checks, and its mineral content matters far less than how much your cat actually drinks. Bottled water brings nothing extra, and a fountain filter works on taste and residues, not on minerals.
Tap, filtered or bottled: what water should you give your cat?
For a healthy cat, tap water changed every day is the benchmark, and every other option is judged against it. A filter improves the taste and removes whatever is floating in it; bottled water, once opened, changes almost nothing.
The table below compares the four types of water most often given to cats, and what each one really changes in the bowl.
| Water offered | What it changes | Its limitation | When it makes sense |
|---|---|---|---|
| Tap water, changed daily | Your local mineral content, already monitored | A taste of chlorine in the first few hours after it’s drawn | The general case, anywhere in France |
| Tap water filtered by a fountain | Same minerals, a milder chlorine taste, moving water | The filter removes neither calcium nor magnesium | Cats fussy about taste, heavily chlorinated water |
| Bottled spring or mineral water | A known mineral content, shown on the label | No proven benefit in healthy cats, and the water quickly gets dirty once the cap is off | Emergencies, water cuts, travel |
| Water from a home water softener | Much less calcium and magnesium | The calcium is replaced with sodium | Avoid by default: use unsoftened tap water instead |
The real difference isn’t what’s in the water, but the state it’s in. Water that has sat still for twelve hours in a narrow bowl will be snubbed, whether it came from the tap or from a bottle of mountain spring water. That’s exactly what a continuously filtering fountain fixes: it keeps the water circulating and clears out hair and dust throughout the day, without anyone having to think about it.
How to find out the hardness and mineral content of your local water
In France, the composition of your local water can be checked online for free, with no lab test to pay for. The ministry of health publishes the health-check test reports for each municipality on eaupotable.sante.gouv.fr (in French). The raw data behind those reports has been republished as open data on data.gouv.fr (in French) since 1 January 2016, under the Open Licence 2.0 and updated monthly — but as archives of several hundred megabytes, best left to anyone who wants to process the files themselves.
On a test report, hardness is expressed in French degrees (°f). According to France’s Water Information Centre (CIEau) (in French), one French degree corresponds to 4 mg of calcium or 2.4 mg of magnesium per litre, and water is described as hard above 15 °f.
So water at 30 °f provides at most 120 mg of calcium per litre — less in reality, since part of that hardness comes from magnesium rather than calcium. A 4 kg cat who drinks 200 ml therefore takes in 24 mg at most — to be weighed against what their daily food provides, which remains their main source of minerals by a very long way.
On a bottle, the same reading comes down to four lines on the label:
- Dry residue at 180 °C: everything that’s left after evaporation, in mg per litre. It’s the total mineral content, the first figure to look at.
- Calcium and magnesium: the two minerals that make up hardness, also given in mg per litre.
- Sodium: the line that tells a neutral-tasting water from a very salty one.
- Nitrates: almost always listed in mg per litre on French spring and mineral waters — it’s the line parents check when they’re looking for water for a baby’s bottle. For tap water, the figure is in your municipality’s test report.
Is hard water a problem for cats?
Hard water is no reason to switch water for a healthy cat. The CIEau points out that French regulations set no maximum limit for calcium concentration in tap water, and that hard water has no consequences for human health.
Where limescale really shows is on equipment. In a hard-water area, white deposits appear on a fountain’s pump and basin within two to three weeks — that’s a matter of fountain maintenance, not of feline health.
Cats with a history of urinary problems are a different matter, and not one a blog post can settle. If your cat has already had stones, blood in their urine or repeated unproductive trips to the litter tray, it’s your vet who decides what food and water to give them, based on their own tests. No shop-bought water replaces that advice.
Water that still tastes of water
Ceramic doesn’t hold on to odours or tastes, and it doesn’t scratch — and it’s micro-scratches that harbour biofilm and end up changing the taste of the water. See the ceramic fountain →
What does a water fountain filter really remove?
A fountain filter removes what floats and some of what smells: hair, dust, food residue, and the chlorine behind that swimming-pool taste. It removes neither calcium, nor magnesium, nor nitrates.
It’s a common mix-up, and it gets expensive in cartridges: “filtered water” doesn’t mean “softened water”. An activated carbon cartridge works on taste, clarity and particles, not on mineral content. A cat who turns up their nose at heavily chlorinated water will change their mind with a filter; the hardness reading in French degrees, on the other hand, won’t budge.
A saturated cartridge releases what it has trapped and becomes a breeding ground for bacteria. How often to replace it depends on the number of cats, the length of their coats and the hardness of the water — the details are in the cleaning guide, and the choice of basin material in the ceramic or plastic comparison.
Why the amount they drink matters more than the type of water
How much they drink is the only factor that makes a difference over the course of a day. According to the Royal Canin Academy, a cat needs around 50 ml of water per kilo per day, so 200 to 250 ml for a 4 to 5 kg cat, from all sources combined.
“From all sources combined” changes everything. Wet food contains around 80% water, dry kibble 10% at most. A cat fed only on dry food therefore has to get almost all of those 200 ml from the bowl; a cat on wet food drinks a fraction of it and does perfectly well.
The same source also notes that cats’ supposed preference for running water wasn’t confirmed by the survey of owners: individual differences win out. Nearly 60% of the cats observed drank, daily or occasionally, somewhere other than their bowl — a watering can, a plant pot, a container meant for humans.
Three adjustments count for more than the choice between tap and bottled: a bowl wide enough for the whiskers not to touch the sides, a spot away from the food bowl and the litter tray, and several water stations around the home. All three are covered in detail in my cat won’t drink and in the guide to where to put the fountain.
To be honest, if your cat eats wet food, drinks normally and has no history of urinary problems, switching water won’t gain you anything. The subject deserves your attention when they eat dry food, when they visibly drink little, or when they refuse water that’s sitting still in a bowl — and then it’s the set-up that needs rethinking, not the bottle, as the fountain or bowl comparison explains.
Frequently asked questions
Can a cat drink water from a home water softener?
It’s best avoided by default. A water softener works by ion exchange: it removes calcium and magnesium and replaces them with sodium, which makes the water less hard but saltier. Most installations leave one unsoftened tap in the kitchen: that’s the one to use when filling your cat’s bowl or fountain. If in doubt, especially if your cat is on a prescription diet, ask your vet.
Should you boil your cat’s water?
No. French tap water is already monitored, and boiling it solves none of the problems people attribute to it. It doesn’t usefully remove limescale: it makes it precipitate, and it settles as scale at the bottom of the pan, as in a kettle. As for nitrates, boiling concentrates them, since the water evaporates and they don’t. It does drive off chlorine, but a simple container left open for an hour does the same with no effort. And boiled water that’s been cooled and left out all day turns back into a bacteria soup like any other.
Is rainwater or puddle water risky?
Neither is checked in any way: run-off from roofs, gutter residue, garden chemicals, bird droppings. An outdoor cat will drink some now and then without it being a disaster, but it should never become their main water source or a “trick” to get them drinking more. If a cat always prefers a puddle to their bowl, the problem is the bowl, not the puddle.
Should you change your cat’s water after moving house?
No, but it’s worth looking at the new local water report: going from water at 10 °f to water at 35 °f changes the taste and markedly speeds up scaling in a fountain. Some cats snub their bowl for a few days after a move — that’s usually down to stress and the change of surroundings, not the water. Keeping the same bowl in the same relative spot helps more than changing the water.
Key points
- Tap water, changed every day, is fine for a healthy cat anywhere in France; bottled water has no proven benefit for healthy cats.
- In France, the hardness and mineral content of your local water can be checked for free in the health-check results published by the ministry of health: 1 °f equals 4 mg of calcium or 2.4 mg of magnesium per litre, and water is hard above 15 °f.
- A fountain filter works on chlorine, hair and particles — never on calcium, magnesium or nitrates.
- A cat needs around 50 ml of water per kilo per day from all sources combined, and wet food is around 80% water, compared with 10% at most for dry kibble.