# How Do You Calculate Water Resistance?

Here at the Gateway Cable Company we’re proud to sell a wide variety of products for use in the military, agriculture, and the automotive industry. We may not have a water resistance calculator, but we understand that some may be asking, “how do you calculate water resistance?” We’ve written the guide below to show you and other residents how.

## What is Water Resistance?

Before we explain how you can measure water resistance, it helps to establish a base understanding by answering, “What is water resistance?” Water resistance, or the resistivity of water, is the ability of water to resist electrical current. Water resistance correlates with the levels of dissolved salt in the water. Remember this: a higher concentration of dissolved salt in the water correlates with a low resistance to electrical current, while a lower concentration of dissolved salt in the water correlates with high resistance to electrical current.

## When Would I Need To Calculate Water Resistance

Understanding when to calculate water resistance depends on the application. For example, certain industrial processes require ultra-pure water. Measuring the resistance of the water could inform you of the concentration of dissolved salt and potential contaminants in the water. If you perform the calculation for water resistance and find a high resistance to electrical current, that would indicate purer water, and vice versa.

## What Tools Do I Need to Calculate Water Resistance?

In order to calculate water resistance in your system, you’ll need to use the Lohm law for liquid flow. As long as you are measuring water and using units of psi for pressure and gpm for flow, this is a fairly simple calculation to perform, but you may still be asking “what tools do I need to calculate water resistance?” You’ll only need three:

• A Differential Pressure Meter
• A Water Flow Meter
• A Calculator

You should be able to find all three or be able to order them for delivery directly to your home. Look below for our explanation of the Lohm law for liquid flow, and how you will use these tools to calculate water resistance. Once you can do it yourself, you won’t need a water resistance calculator.

## How to Calculate Water Resistance

Once you have the appropriate tools, you’ll need to find the variables necessary to perform the calculation. The variables of the Lohm law of liquid resistance are:

• I = Flow Rate
• H = Differential pressure
• V = Viscosity correction factor (this will vary by device as it is determined by the interaction between viscosity and device geometry. Use 1.0 for water at 80 degrees F)
• S = Specific Gravity (Use 1.0 for water at 80 degrees F)
• K = A constant (This value takes units of measure into account. Use 20 for psi and gpm)

Since you are calculating the resistance of water, you’ll only need to find two of these variables: I and H. However, for the sake of understanding, here is the full equation for calculating liquid resistance, otherwise known as Lohms.

Like we said, you are calculating the resistance of water. This allows you to use the value 1 for variables V and S, and as long as you use the units of psi and gpm, K will equal 20. That leaves the equation.

Now the only values you need to measure are the differential pressure and the flow rate. To calculate water resistance, just follow these steps:

1. Use your Differential Pressure Meter to measure the differential pressure in your system. Record it in the unit psid
2. Use your Water Flow Meter to measure the flow rate within your system. Record it in the unit gpm.
3. Input these values into the I and H positions of your equation and calculate using a calculator.

Memorize this equation, and you’ll never need a water resistance calculator.