How to Increase the Density of Water
Increasing the density of water can be achieved primarily by two methods: adding dissolved substances or decreasing its temperature.
Adding solutes, such as salt, increases the water's density. This is because the added mass of the solute increases the overall mass of the solution without significantly increasing its volume. The more solute you add, the denser the water becomes, up to the point of saturation.
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Example: Adding salt to water creates a saltwater solution. The density of saltwater is higher than that of freshwater. As noted in multiple sources (Salt Water Density Experiment, Density, Temperature, and Salinity), this increase in density is due to the added mass of the salt. A saturated solution of sodium chloride in water can achieve a density of around 2.16 g/cm³ (Can I increase the density of water to above 1.5?).
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Other Solutes: Other substances can also increase water density, though the effect varies depending on the solute's solubility and molecular weight.
Increasing Density by Lowering Temperature
Water's density is also affected by temperature. Water is densest at approximately 4°C. Cooling water below this temperature causes it to expand slightly, decreasing its density. (Lesson 3.6: Temperature Affects Density) This is an unusual property of water.
- Practical Limitation: While lowering temperature can increase density (to a maximum at 4°C), it's less effective than adding solutes for significantly increasing density.
Limitations
It's important to note that you cannot arbitrarily increase water density to any desired level. The maximum density achievable depends on the solubility of the added substance and the physical properties of water. As stated in How to increase the density of water 1.5 times - Quora, simply increasing the density of water 1.5 times under normal atmospheric conditions is not possible.
