What’s the Difference Between DI Water and Tap Water?

Wondering what the difference is between DI water and tap water?)

You probably already know that for certain applications, it’s essential to use deionized water instead of tap. But why? What are the major differences between DI water and tap water, and why are they so important?

The answer to this question, in some cases, can actually be a matter of life and death. For instance, if you manufacture injectable medication using regular tap water, it could place a patient at imminent risk. To understand why, we’ll need to explain exactly what tap water is, the different kinds, and how the deionization process changes it.

Breaking Down Tap Water – What It Is, Where it Comes From

Tap water can come from one of two sources: groundwater or surface water. We take both of these water sources into account when designing a purified water system. The varying characteristics between the sources (ground and surface) will impact the deionization process differently.

1. Groundwater

Groundwater comes from rain water that seeps through the layers of soil, rock and minerals, eventually depositing in an underground aquifer. This water is retrieved through a well and a pump. Here are the three defining characteristics of groundwater:

Total Dissolved Solids (TDS): Average 300 – 600 TDS

Organic content: Normally lower than surface water based on less microbial content.

Chemistry makeup: The water’s chemistry will reflect that of the ground it permeates, including the rock, stone and minerals it flows through, on it’s way to the aquifer. Water is a natural solvent, it breaks down a small amount of everything it comes in contact with.

2. Surface water

The other primary source of tap water is surface water, which we pull off the surface of a freshwater source, such as a lake or a river. Here are the three defining characteristics of surface water:

Total Dissolved Solids (TDS): Average 100 – 200 TDS

Organic content: Generally higher than groundwater because it has more living organisms and microorganisms living in it, like fish and algae. For this reason, the water is also typically more turbid.

Chemistry makeup: The chemistry will reflect the surface area of wherever the lake or river is located. This includes sodium from runoff as well as leaves and other debris that flow into the water.

While tap water is generally fine for drinking, other applications require a more highly purified water.

Turning Tap Water Into Deionized Water

Water in its purest form consists of Hydrogen (H+) and Hydroxyl (OH-) ions, which combine to create H2O. When considering a water’s purity, anything found in water other than the Hydrogen and Hydroxyl ions, are an impurity.

Bacteria, minerals, charged ions, pharmaceuticals, caffeine, fertilizers, volatile organic compounds (VOCs), cleaning agents, debris or anything else we’ve introduced into our water system, is an impurity.

The process of deionization exchanges all of the charged ions found in tap water for Hydrogen and Hydroxyl ions. This process helps to form the water molecule, H2O. The deionization or ion exchange process results in a true purified water “blank,” nothing but water in its purest form.

The deionized water will then take on the characteristics of any solution or chemistry that is added to it. Good quality deionized water will measure approximately 18.2 megohms resistivity with a temperature compensated resistivity meter.

So how do we get there? It involves a deionization process that uses high purity resin to initiate an exchange cycle, cleansing the water of unwanted ions. However, the configuration of equipment for this process varies widely depending on several factors.

1. Type of tap water

Deionizers have a lower capacity for purification of groundwater than that of surface water. That’s because there are normally less charged ions to exchange in surface water than in groundwater (as indicated by the lower TDS).

This means the canisters involved with deionizing surface water will likely last longer than they would for deionizing groundwater.

2. Level of necessary purification

While every deionization system purifies water, the level of purification varies depending on how we configure the process. We customize your deionization system to cater to your specific water application needs.

For instance, we’d configure a deionization system for a client that needs water for medical applications quite differently than a facility that needs deionized water for a glass rinsing application. The purity of deionized water largely hinges on the type of high purity DI resin we use with the system. You can read more about this process here.

3. Water capacity

We generally begin the deionization process by installing a canister, or a set of canisters, that can purify anywhere from a quarter gallon of water per minute all the way up to 500 gallons per minute.

However, if capacity requirements are high, we’ll consider different types of equipment configurations to help improve efficiency.

To really appreciate the importance of deionized water, perhaps it’s best to see several examples of its applications.

Deionized Water in Action

Facilities across a variety of industries require deionized water for a myriad of reasons. Here are just three examples:

Product manufacturing

For this category, we’ll use a glass manufacturer as an example. A glass manufacturer may require DI water to rinse their product after it’s complete.

If they used tap water, the TDS (calcium, magnesium, silica) would show up as spots on the glass when it dries, and could even scratch the glass surface.

Biotech or pharmaceutical applications

Any biotech or pharmaceutical manufacturing facility making a liquid product will normally need to use high purity deionized, bacteria-free water.

They normally add a solution or a chemical mixture to water that may eventually find its way into a patient’s body, so any amount of organic content could jeopardize the product, and thus the patient’s health.

Specimen processing (cleaning of surgical instruments)

Although specialized machines disinfect surgical instruments with a liquid mixture or a disinfecting gas, a microbial-free final rinse with purified water is necessary to cleanse the instruments of any residuals.

Using tap water for the final rinse would not only create spots on the instruments, it could also create trace amounts of organics during the final rinse stage.

Deionized water and tap water vary considerably in composition and application. It’s crucial to choose a water treatment provider who can guide you through the DI configuration process and properly install the right system for your needs.

We’ll do more than give you a quote—we’ll visit your site to analyze your industrial water needs.

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