Water dissolves more substances than any other common liquid, which is why chemists call it the “universal solvent.” It can break apart salts, mix with sugars and alcohols, absorb gases from the atmosphere, and carry minerals through rock, soil, and your bloodstream. The key to water’s dissolving power is its molecular structure: each water molecule has a slight positive charge on one side and a slight negative charge on the other, which lets it pull apart and surround a wide range of chemical compounds.
Why Water Dissolves So Many Things
A water molecule is lopsided. The oxygen atom hogs electrons, giving it a negative charge, while the two hydrogen atoms carry a positive charge. This separation of charge makes water “polar,” and it’s the reason water is such an effective solvent. When a substance enters water, those charged ends go to work. Positive hydrogens attract negatively charged parts of the substance, and the negative oxygen attracts positively charged parts. If water’s pull is strong enough to overcome the forces holding the substance together, the substance dissolves.
This process creates what scientists call a hydration shell: a cluster of water molecules surrounding each dissolved particle, keeping it separated from its neighbors and preventing it from clumping back together. The general rule is simple. Polar substances and charged particles dissolve well in water. Non-polar substances do not.
Salts and Ionic Compounds
The most familiar example is table salt. When salt crystals hit water, water molecules wedge between the positively charged sodium and negatively charged chloride, pulling them apart and surrounding each ion individually. This same process works on a huge number of ionic compounds, though not all of them.
The patterns are well established. All sodium, potassium, and ammonium salts dissolve in water. All nitrate and acetate salts dissolve. Chloride, bromide, and iodide salts dissolve, with a few exceptions: silver, lead, and mercury salts of these tend to stay solid. Sulfate salts generally dissolve too, except when paired with calcium, barium, strontium, lead, silver, or mercury.
On the insoluble side, most hydroxide, carbonate, and phosphate salts resist dissolving. That’s why limestone (calcium carbonate) forms durable rock rather than washing away in the first rainstorm, though very small amounts do dissolve over time, which is how caves form.
Sugars, Alcohols, and Other Polar Molecules
Water doesn’t just dissolve things by ripping apart ions. It also mixes thoroughly with other polar molecules through hydrogen bonding, a kind of weak attraction between hydrogen atoms and oxygen or nitrogen atoms on neighboring molecules. Sugars are a perfect example. Sucrose (table sugar) is extraordinarily soluble: about 200 grams dissolve in 100 milliliters of water at room temperature. That means you can dissolve roughly twice the weight of sugar as the weight of water you’re using. This extreme solubility comes from sucrose’s structure, which has 8 hydrogen bond donors and 11 hydrogen bond acceptors, giving water molecules plenty of places to latch on.
Glucose dissolves readily for the same reasons. Ethanol (drinking alcohol) mixes with water in any proportion because its small molecule has both a polar end that bonds with water and a carbon chain short enough not to interfere. Vinegar (acetic acid), many amino acids, and water-soluble vitamins like vitamin C and the B vitamins all dissolve through similar hydrogen-bonding interactions.
Gases
Water dissolves gases too, though in much smaller quantities than solids. Oxygen dissolves at low concentrations, enough to keep fish and aquatic organisms alive. Carbon dioxide is about 27 times more soluble than oxygen in water at room temperature. When CO₂ dissolves, it reacts with water to form carbonic acid, which is what gives carbonated drinks their slight tang.
Other gases that dissolve in water include nitrogen, hydrogen sulfide (responsible for the rotten-egg smell of some hot springs), sulfur dioxide, chlorine, and ammonia. Ammonia and hydrogen chloride are highly soluble because they react chemically with water once dissolved.
Minerals in Drinking Water
Tap water is never pure H₂O. As water moves through soil and rock, it picks up dissolved minerals. The World Health Organization describes Total Dissolved Solids (TDS) as the sum of inorganic salts and small amounts of organic matter in water. The main dissolved minerals are calcium, magnesium, sodium, and potassium, along with carbonates, chlorides, sulfates, and nitrates.
Natural TDS levels range from less than 30 milligrams per liter in rainwater-fed mountain streams to as much as 6,000 mg/L in regions with highly soluble mineral deposits. Water below 1,000 mg/L is generally considered acceptable for drinking. The mineral content is what gives different water sources their distinct taste. Very low TDS water tastes flat, while moderately mineralized water often tastes crisp or pleasant.
How Water Carries Nutrients in Your Body
Your blood plasma is about 95 percent water, and it works as a solvent for an enormous range of molecules. Dissolved in that plasma at any given time are sugars like glucose, amino acids, minerals, water-soluble vitamins, waste products like urea, hormones, enzymes, and dissolved gases including oxygen and carbon dioxide. Water-soluble molecules move freely and independently through the bloodstream.
Fat-soluble substances, like cholesterol, triglycerides, and vitamins A, D, E, and K, don’t dissolve in water on their own. Your body packages them into special protein-coated carriers called lipoproteins that can travel through the watery environment of blood. This distinction between water-soluble and fat-soluble nutrients shapes how your body absorbs, transports, and stores nearly everything you eat.
What Water Cannot Dissolve
Water fails with non-polar substances: molecules that lack any charge separation. Cooking oils, fats, waxes, gasoline, and most plastics are all non-polar, which is why oil floats on water rather than mixing in. The underlying reason is that water molecules are more attracted to each other than to non-polar molecules. When a non-polar substance enters water, the water molecules tighten their hydrogen-bonding network around it, essentially squeezing it out. Non-polar molecules get pushed together and aggregated, minimizing their contact with water. This is the hydrophobic effect.
This is also why grease won’t wash off your hands with water alone. You need soap, which has one polar end that interacts with water and one non-polar end that grabs onto the grease, bridging the gap between the two.
Temperature Changes What Dissolves
For most solid substances, hotter water dissolves more. That’s why sugar dissolves faster and in greater quantities in hot tea than in iced tea. The increased molecular motion at higher temperatures helps break apart solute particles and makes room for more dissolved material.
Gases behave in the opposite way. As water temperature rises, dissolved gases escape. This is why a pot of water releases small bubbles as it heats on the stove, well before it reaches boiling. It’s also why warm lakes and rivers hold less dissolved oxygen than cold ones, which can stress fish populations during summer heat waves.
Everyday and Industrial Uses
Water’s solvent properties show up everywhere. Coffee and tea are aqueous solutions where hot water extracts flavor compounds, caffeine, and pigments from plant material. Carbonated drinks rely on CO₂ dissolved under pressure. Saline solution is simply salt dissolved in water at a controlled concentration.
In industry, water dissolves strong acids like hydrochloric acid and nitric acid for chemical manufacturing and metal processing. It serves as the solvent in countless cleaning, dyeing, and food-processing operations. Hydrochloric acid dissolved in water is also what your stomach uses to break down food. Water’s ability to dissolve such a broad spectrum of substances, from simple table salt to complex proteins, is what makes it essential to both biology and industry.