The image above represents water activity.

To compute for water activity, two essential parameters are needed and these parameters are **Partial Pressure of Water (P _{w})** and

**Equilibrium Vapour Pressure of Water at Same Temperature (V.P.**

_{w}).The formula for calculating water activity:

a_{w} = ^{Pw}/_{V.P.w}

Where:

a_{w} = Water Activity | Drying

P_{w} = Partial Pressure of Water

V.P._{w} = Equilibrium Vapour Pressure of Water at Same Temperature

Let’s solve an example;

Find the water activity when the partial pressure of water is 22 and the equilibrium vapour pressure of water at same temperature is 28.

This implies that;

P_{w} = Partial Pressure of Water = 22

V.P._{w} = Equilibrium Vapour Pressure of Water at Same Temperature = 28

a_{w} = ^{Pw}/_{V.P.w}

a_{w} = ^{22}/_{28}

a_{w} = 0.78

Therefore, the **water activity **is **0.78.**

**Calculating the Partial Pressure of Water when the Water Activity and the Equilibrium Vapour Pressure of Water at Same Temperature is Given.**

P_{w} = a_{w} x V.P._{w}

Where;

P_{w} = Partial Pressure of Water

a_{w} = Water Activity | Drying

V.P._{w} = Equilibrium Vapour Pressure of Water at Same Temperature

Let’s solve an example;

Find the partial pressure of water when the water activity is 24 and the equilibrium vapour pressure of water at same temperature is 14.

This implies that;

a_{w} = Water Activity | Drying = 24

V.P._{w} = Equilibrium Vapour Pressure of Water at Same Temperature = 14

P_{w} = a_{w} x V.P._{w}

P_{w} = 24 x 14

P_{w} = 336

Therefore, the **partial pressure of water **is **336.**

**Calculating the Equilibrium Vapour Pressure of Water at Same Temperature when the Water Activity and the Partial Pressure of Water is Given.**

V.P._{w} = ^{Pw} / _{aw}

Where;

V.P._{w} = Equilibrium Vapour Pressure of Water at Same Temperature

a_{w} = Water Activity | Drying

P_{w} = Partial Pressure of Water

Let’s solve an example;

Find the equilibrium vapour pressure of water at same temperature when the water activity is 10 and the partial pressure of water is 30.

This implies that;

a_{w} = Water Activity | Drying = 10

P_{w} = Partial Pressure of Water = 30

V.P._{w} = ^{Pw} / _{aw}

V.P._{w} = ^{30} / _{10}

V.P._{w} = 3

Therefore, the **equilibrium vapour pressure of water at same temperature **is **3.**

Nickzom Calculator – **The Calculator Encyclopedia** is capable of calculating the water activity.

To get the answer and workings of the water activity using the **Nickzom Calculator – The Calculator Encyclopedia. **First, you need to obtain the app.

You can get this app via any of these means:

**Web** – https://www.nickzom.org/calculator-plus

To get access to the **professional **version via web, you need to **register** and **subscribe **for** NGN 2,000 **per** annum** to have utter access to all functionalities.

You can also try the **demo **version via https://www.nickzom.org/calculator

**Android (Paid)** – https://play.google.com/store/apps/details?id=org.nickzom.nickzomcalculator

**Android (Free)** – https://play.google.com/store/apps/details?id=com.nickzom.nickzomcalculator

**Apple (Paid)** – https://itunes.apple.com/us/app/nickzom-calculator/id1331162702?mt=8

Once, you have obtained the calculator encyclopedia app, proceed to the **Calculator Map, **then click on **Materials and Metallurgical **under **Engineering****.**

Now, Click on **Ball Mill Sizing**** **under **Materials and Metallurgical**

Now, Click on **Water Activity**** **under **Ball Mill Sizing**

The screenshot below displays the page or activity to enter your values, to get the answer for the water activity according to the respective parameters which is the **Partial Pressure of Water (P _{w})** and

**Equilibrium Vapour Pressure of Water at Same Temperature (V.P.**

_{w}).Now, enter the value appropriately and accordingly for the parameter as required by the **Partial Pressure of Water (P _{w}) **is

**22**and

**Equilibrium Vapour Pressure of Water at Same Temperature (V.P.**is

_{w})**28**.

Finally, Click on Calculate

As you can see from the screenshot above, **Nickzom Calculator**– The Calculator Encyclopedia solves for the water activity and presents the formula, workings and steps too.