Let’s explore the density of water!

What is the density of water? Do you have any idea! In this post, we will learn the basics of water density in pure or freshwater, sea or saltwater along with room temperature, at 25 c, to get a clear concept.

Let’s explore!

Water density, the most widely used term in fluid mechanics. We will understand the basics along with water density definitions and examples.

Water density is widely used to identify pure water as well as all other forms of water at different temperatures. We use water in various applications, various industries. We will see here how water density is defined, measured, utilized.

Take one liter of water and one liter of gasoline. What do you think which one will be heavy? Or which one will be lighter?

By weighing, gasoline will be lighter than water. We can say, the mass of 1liter of water is heavier than the mass of 1 liter of gasoline.

Similarly, if we take some amount of honey, gasoline & water and kept in a beaker, we will see,

- First layer: Honey, as it is heaviest upon three
- Second layer: Water, as it is lighter than honey but heavier than gasoline
- Third layer: Gasoline, which is the lightest of three.

This is simply the concept of density of water or gasoline or honey or any others.

Basically density of water means,

- Mass of water per unit volume

Let’s delve into the definition of water density!

The water density is defined as the mass per unit volume.

Water Density = Mass of water/Volume of water

- Water density means intensive property, as there will not be any change with respect to an increase in mass or volume.
- The density of water is different at different temperatures.
- Water density is the property of the water.
- If the mass of water per unit volume decreases, then the density will decrease, and if the mass of water per unit volume increases, then the density will increase.
- It indicates how tightly the water molecules are packed or adhere to each other.
- If water molecules are too close then the density will be more and if water molecules are distant from each other, then the density will be less.

Normally, ρ is used to indicate the density of water. Many times, ‘D’ or ‘d’ is also used to represent the water density.

Let’s try to look at the formula of water density or a simple equation of density.

Take some water and consider,

- ρ = Density of water
- m = Mass of water
- V = Volume of water

From the definition of water density,

we write,

The density of water = Mass of Water/Volume of Water

ρ = m/V

Now,

If V = 1, ρ = m.

From this, we can say, if volume = unit, then the water density will be equal to mass.

**Water density in SI unit**

- kg per cubic meter (kg/m
^{3}), value = 1000 kg/m^{3}

**Water density in C.G.S unit**

- gm per centimetre (g/cm
^{3}), value = 1 g/cm^{3}

**Water density in F.P.S unit**

- pound per cubic foot (lb/ft
^{3}), value = 62.4 lb/ft^{3}

**Water density in Other Units**

- kilogramper litre (kg/L)
- gram per cubic centimeter (g/cm
^{3}) - metric ton per cubic meter (t/m
^{3}) - gramper millilitre (g/mL)
- 1 g/cm
^{3}= 1000 kg/m^{3}

In studying water density, we will see how to find or measure the density of water.

So, how to find it?

**Step#1**

Take a container of having a volumetric mark to get the data of volume. Let’s consider the size of the container is 25cm x 18cm x 15cm and it is filled with water.

Hence, volume,

v = 25 cm x18 cm x 15 cm

v = 0.25 m x 0.18 m x 0.15 m

v = 0.25 x0.18 x 0.15

v = 0.00675 m^{3}

**Step#2**

Measure the mass of water, it is 6.75 kg.

**Step#3**

The density of water = Mass of Water/Volume of Water

The density of water = 6.75 / 0.00675

The density of water = 1000 kg/m^{3}

Thus, the density of water is 1000 kg/m^{3}.

The density of water sometimes behaves unusually. We can see the behavior of water density pointwise,

- If we cool water vapor, it will form water and its density will increase. [Normal behavior, as density, is increasing from vapor to liquid]
- Further cooling of water forms ice and its density decreases. [Abnormal behavior, as density, is decreased instead of increasing]

The factors are:

- Salinity
- Temperature

Salinity

- Water density increases with the increase of salinity.
- In this case, water molecules are packed with salts and the water will be densed.
- The high density of saline water i.e. seawater allows us to float easily.
- Its density is more than pure water.

Temperature

Let’s check the water density with temperature chart,

- If water temperature is reduced, then the water molecule’s motion will be reduced.
- Reduction of motion will help them to make the gap between molecules.
- Due to this gap, water molecules will create more hydrogen bonds.
- This creates space and density will reduce.

The density of water varies with temperature from EngineeingToolbox, as follows

Temperature | Density (0-100°C at 1 atm, >100 °C at saturation pressure) | |

[°C] | [g/cm^{3}] |
[kg/m^{3}] |

0.1 | 0.9998495 | 999.85 |

1 | 0.9999017 | 999.90 |

4 | 0.9999749 | 999.97 |

10 | 0.9997000 | 999.70 |

15 | 0.9991026 | 999.10 |

20 | 0.9982067 | 998.21 |

25 | 0.9970470 | 997.05 |

30 | 0.9956488 | 995.65 |

35 | 0.9940326 | 994.03 |

40 | 0.9922152 | 992.22 |

45 | 0.99021 | 990.21 |

50 | 0.98804 | 988.04 |

55 | 0.98569 | 985.69 |

60 | 0.98320 | 983.20 |

65 | 0.98055 | 980.55 |

70 | 0.97776 | 977.76 |

75 | 0.97484 | 974.84 |

80 | 0.97179 | 971.79 |

85 | 0.96861 | 968.61 |

90 | 0.96531 | 965.31 |

95 | 0.96189 | 961.89 |

100 | 0.95835 | 958.35 |

110 | 0.95095 | 950.95 |

120 | 0.94311 | 943.11 |

140 | 0.92613 | 926.13 |

160 | 0.90745 | 907.45 |

180 | 0.88700 | 887.00 |

200 | 0.86466 | 864.66 |

220 | 0.84022 | 840.22 |

240 | 0.81337 | 813.37 |

260 | 0.78363 | 783.63 |

280 | 0.75028 | 750.28 |

300 | 0.71214 | 712.14 |

320 | 0.66709 | 667.09 |

340 | 0.61067 | 610.67 |

360 | 0.52759 | 527.59 |

373.946 | 0.3220 | 322.0 |

It is required to know the water density at room temperature for many applications,

Now room temperature can be 20 ^{o}C or 25 ^{o}C based on the inside design temperature or HVAC design. We will see both the temperature from the table just for ready reference.

Room Temperature | Density of Water | |

[°C] | [g/cm^{3}] |
[kg/m^{3}] |

20 | 0.9982067 | 998.21 |

25 | 0.997047 | 997.05 |

So, we can say,

- Water density at 20
^{o}C = 0.9982067 [g/cm^{3}] or 998.21 [kg/m^{3}] - Water density at 25
^{o}C = 0.9972047 [g/cm^{3}] or 997.05 [kg/m^{3}]

There are many devices available to measure the density of water, as follows

- Hydrometer
- Pycnometer
- Oscillating densitometer
- Dasymeter
- Coriolis flowmeter

One well-known application of density is determining whether or not an object will float on water. If the object’s density is less than the density of water, it will float; if its density is less than that of water, it will sink.

Hence, we have got a basic concept of water density in pure or freshwater, sea or saltwater along with room temperatures, like 20^{o}C or 25^{o}C, to get a clear concept.

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