Saliva is about 99% water. The other 1% is doing almost all the work. It lubricates, it neutralises acid, it repairs your teeth and it keeps the bacteria in your mouth in check. This is why a dry mouth causes problems that drinking water never solves. Water gives you the 99% and none of the 1%.
Where it comes from
You have three pairs of major salivary glands and they don't do the same job.
The parotid glands sit just in front of your ears. They produce thin watery saliva and they are the ones that flood your mouth when you smell food or bite into something sharp. Most of the time they are fairly quiet.
The submandibular glands, under your jaw, are the workhorses. They produce most of your background saliva, the steady supply that keeps your mouth comfortable when you aren't eating, including overnight.
The sublingual glands, under your tongue, produce a small amount of thick slippery saliva that does far more coating and comforting than its volume suggests.
Then there are several hundred tiny minor glands scattered through your lips, cheeks and palate, quietly keeping the surfaces wet.
Something neat happens between them. They swap leadership. At rest, the submandibular glands provide around two-thirds of your saliva. When you chew, the parotids take over and can produce more than half. Your mouth has a resting mode and an eating mode, run by different glands.
Altogether most people produce somewhere in the region of half a litre to a litre and a half a day, though you will see far more confident-sounding numbers quoted online than the research actually supports.
What is actually in it
Roughly 99% water. The interesting part is the rest.
Mucins are long slippery molecules that stick to your tissues and hold water. They are the reason saliva coats your mouth and stays there rather than simply running off, and they are also what makes saliva stringy when you are dehydrated. If you have noticed that a mouthful of water disappears instantly while normal saliva seems to linger, mucins are the difference.
Bicarbonate is a natural antacid. It neutralises the acid produced when bacteria feed on sugar, and it is the reason your mouth recovers after a meal instead of staying acidic all day.
Calcium and phosphate are the building blocks of your teeth, and saliva carries them in a dissolved, ready-to-use form. Your teeth are being repaired constantly, from a supply in your own saliva.
A set of protective proteins, with names like lysozyme, lactoferrin and histatins, break down bacteria, starve them of iron and hold fungal infections such as thrush in check. There are also antibodies, the same immune molecules found elsewhere in your body.
Enzymes start digesting your food before you have swallowed it.
That tiny fraction is the difference between saliva and water.
What saliva does all day
It keeps everything moving. Your tongue moves against your teeth and cheeks thousands of times an hour. Saliva forms a thin film that keeps those surfaces gliding rather than dragging, which is why you can talk for an hour without noticing.
It protects your teeth from acid. Every time you eat something with sugar or starch in it, the bacteria in your mouth produce acid and the acidity in your dental plaque drops within minutes. Below a certain point your enamel starts dissolving. Saliva reverses this, diluting the sugar, washing it away and neutralising the acid with bicarbonate. It usually takes half an hour to an hour for things to return to normal.
Something curious happens when you chew. Chewing roughly doubles how much saliva you produce, but it increases the amount of bicarbonate coming out by around nine times. The buffering system doesn't just scale up with the volume, it goes into a different gear. This is why chewing sugar-free gum after a meal helps, and it has nothing to do with the gum itself.
It repairs your teeth. Once the acid has been neutralised, the calcium and phosphate in your saliva get redeposited into the enamel surface. Small amounts of damage are repaired every single day, silently, by a fluid you never think about.
There is a lovely problem hidden in this. If saliva is packed with dissolved tooth minerals, why doesn't it simply solidify in your mouth? Because it carries specific proteins whose entire job is to stop that happening. They hold the minerals in solution, available but not precipitating. Saliva carries your repair material in suspension, permanently ready.
It manages the bacteria. Note the word: manages. Your mouth is meant to have bacteria in it. Saliva doesn't sterilise it, it dilutes, washes away, clumps together and keeps the balance tipped in your favour. When saliva drops, the balance shifts towards the species that cause decay and thrush.
It lets you taste. Flavour molecules have to dissolve before your taste buds can detect them, and then be cleared away before the next mouthful. A dry mouth mutes taste at both ends of that process, which is why food can go flat in a way people rarely connect to saliva.
It lets you swallow. Saliva binds chewed food into a single cohesive lump that can move smoothly. Without enough of it, dry food simply won't go down. This isn't fussiness, it is mechanics.
It coats your teeth within seconds. Proteins from saliva form an invisible film on your teeth almost immediately, which is why they feel slippery after a clean. That film slows acid getting through to the enamel. It is also, honestly, what bacteria attach to first, so it protects and provides a foothold at the same time.
It protects below the mouth too. When acid comes up from your stomach, swallowing clears most of it and bicarbonate in your saliva neutralises the film left behind on your oesophagus.
Why it is worse at night
Because saliva production falls dramatically while you sleep, by something in the region of 80 to 90% compared with resting during the day.
It makes sense when you think about it. You aren't eating, tasting, chewing or swallowing much, and the part of your nervous system that keeps saliva flowing quietens down along with everything else. If you also breathe through your mouth, evaporation adds to it.
This is the physiological reason behind something people describe constantly: waking at three in the morning with the tongue stuck to the roof of the mouth, drinking the water by the bed, and being exactly as dry ten minutes later. Your glands are running at a fraction of their daytime rate, and a sip of water doesn't change that.
One common claim is worth correcting. The glands don't switch off, they slow right down. That is a meaningful difference when it comes to what might help.
On ageing, getting older by itself has a smaller effect on saliva than most people assume. What rises with age is the number of medicines people take and the number of conditions they have, and those explain a great deal of the association. Ageing alone is not why your mouth is dry.
What happens when it isn't there
The problems arrive in a fairly predictable order, which is useful because it tells you roughly where you are.
Within hours comes stickiness or burning, thirst, your tongue catching on the roof of your mouth, and the sense that your cheeks are sticking to your teeth.
Within days, talking becomes tiring. Dry food is difficult and you find yourself needing a drink with every mouthful. Taste dulls or goes strange. Your lips crack, your tongue may look smoother or redder than usual, and small ulcers appear from ordinary friction.
Within weeks, plaque builds up faster, food gets trapped, breath gets worse, dentures stop fitting comfortably and thrush becomes more likely.
Within months comes decay, and this is the one that matters most, because it is the one you can't feel coming.
Decay in a dry mouth looks different from ordinary decay. It shows up in bands around the necks of teeth at the gum line, on exposed roots, and at the biting edges and tips of teeth, places that normally hold up perfectly well.
The reason it appears in those particular spots is that they are normally protected by being constantly washed, coated and remineralised. Take the saliva away and they lose the only defence they had.
This is why a dry mouth is a dental problem rather than just a comfort problem, and why it is worth mentioning to your dentist even if it doesn't feel urgent.
Why water doesn't fill the gap
Everything above explains it. Water gives you the 99% and none of the 1%.
It doesn't stay, because there are no mucins to make it stick. It can't neutralise acid, because there is no bicarbonate in it. It can't repair enamel, because it isn't carrying dissolved tooth minerals. It has none of the protective proteins, and it can't rebuild the film on your teeth.
There is a measurement that makes this vivid. In a laboratory model measuring how long different fluids kept surfaces in the mouth sliding smoothly, water managed around 25 seconds. Real saliva, the thick mucin-rich kind, managed around 11 to 12 minutes.
The part that surprised the researchers was that the thick low-volume saliva outperformed the watery high-volume kind by a wide margin. More fluid didn't mean better protection, because wetness and lubrication turn out to be completely different things.
That is a laboratory finding rather than a measurement of your actual mouth, so treat the numbers as illustrative. The gap is enormous and the direction isn't in doubt.
A few things about saliva that surprise people
- Your glands swap roles depending on whether you are eating or resting.
- Chewing roughly doubles how much saliva you make, but increases its acid-neutralising power about ninefold.
- Saliva is deliberately loaded with dissolved tooth minerals, and carries specific proteins to stop them solidifying.
- A protective film forms on your teeth within seconds of saliva touching them.
- In a lab test, water kept things slippery for 25 seconds. Real saliva managed nearly twelve minutes.
- Saliva doesn't kill the bacteria in your mouth. It manages them, and you are meant to have them.
- When saliva is very low, decay appears on the parts of teeth that are normally the most resistant.
- Saliva protects your oesophagus after reflux, not just your mouth.
What it comes down to
Saliva isn't just wetness. It is a lubricant, an antacid, a repair system and part of your immune system, produced continuously by glands that change their output depending on what you are doing.
Almost every problem a dry mouth causes traces back to losing one of those four jobs, which is also why the answer is never simply more fluid.
Sources
- Sreebny LM. Saliva in health and disease: an appraisal and update. 2000.
- StatPearls. Physiology, Salivation. 2023.
- Physiological regulation of oral saliva ion composition. 2024.
- Schlesinger & Hay. Statherin: concentration and function. 1984.
- Dawes C. A mathematical model of salivary clearance of sugar from the oral cavity. 1983.
- Acquired pellicle review. Journal of Dental Research. 2012.
- Vinke et al. Ex-vivo salivary lubrication system: tongue and enamel friction model. 2018.
- Amerongen & Veerman. Saliva: the defender of the oral cavity. 2002.
- Salivary flow and oral status in primary Sjögren syndrome. 2023.
- Radiation-induced dental caries review. 2016.
About this article. Written by Dr Jimmy Matloob, dentist. Published 20 September 2026. Last reviewed 20 September 2026.
This is general information about dry mouth. It is not advice about your individual situation, and it is not a substitute for being seen. If something here sounds like you, raise it with your dentist, doctor or pharmacist.
ELVA makes an alcohol-free dry mouth spray.