Deionized (DI) water is a highly purified form of water with nearly all mineral ions removed through deionization or demineralization. These ions, such as calcium, sodium, and chloride, are typically found in tap water and can cause issues like mineral buildup or electrical conductivity. Because DI water lacks these charged particles, it is widely used where high purity is mandatory. Applications include specialized cleaning tasks, laboratory experiments, automotive cooling systems, and electronics manufacturing. Locating a reliable source requires understanding the different types of purified water available to ensure the correct product is acquired.
Understanding Deionized Water vs. Other Types
The term “pure water” can refer to several different products, and it is important to distinguish deionized water from its common counterparts, distilled and reverse osmosis (RO) water. Deionized water is created by passing water through ion exchange resins that chemically attract and swap out positive and negative ions, replacing them with hydrogen and hydroxyl ions, which then combine to form water. This process is exceptionally effective at reducing the water’s conductivity, often achieving levels as low as 0.055 microSiemens per centimeter (\(\mu\text{S}/\text{cm}\)).
Distilled water, in contrast, is produced by boiling water and condensing the resulting steam, leaving behind dissolved solids and minerals. While this removes many impurities, it may not effectively eliminate volatile organic compounds or dissolved gases. Its conductivity is typically higher than DI water, often between 1 and 5 \(\mu\text{S}/\text{cm}\).
Reverse Osmosis water is created by forcing water through a semipermeable membrane, which physically filters out up to 99% of dissolved solids. RO water typically retains more trace ions than DI water, showing a higher conductivity in the range of 5–50 \(\mu\text{S}/\text{cm}\). RO is often used as a pre-treatment before final deionization for maximum purity.
Retail and Consumer Access Points
For small-scale or occasional needs, the most convenient sources for deionized water are often common retail stores that cater to specific consumer markets. Automotive supply stores are a reliable option, as they frequently stock DI water for use in lead-acid batteries and cooling systems where mineral buildup is undesirable. It is important to look for products clearly labeled as “deionized water” or “battery water,” as distilled water is often sold alongside it.
Some large grocery stores and major pharmacies also carry purified water, typically shelving it near bottled drinking water or household cleaning supplies. While many of these bottles contain distilled water, some brands offer deionized water. Careful label reading is necessary to confirm the purification method, ensuring the product description mentions deionization or demineralization rather than solely distillation.
Advanced Acquisition Methods and Bulk Sourcing
When the required application demands higher purity grades or larger volumes, consumers and small businesses must look beyond standard retail shelves toward specialized suppliers. Scientific and laboratory supply companies are a primary source for the highest-grade deionized water, which is often classified using standards like ASTM Type I, II, or III. Type I is the ultrapure grade necessary for sensitive analytical testing, while Type II and III are suitable for general lab work and rinsing. These suppliers offer water in various containers, from single gallons to large drums or totes.
Another option for bulk access is through specialized water bottling or industrial chemical suppliers. These companies frequently cater to industries needing large quantities for manufacturing or heat transfer systems. They can provide water in 55-gallon drums or 275-gallon totes, offering a cost-effective solution for consistent, high-volume use. When ordering from these sources, specify the desired purity, often measured in conductivity, to ensure the water meets the application’s technical requirements.
Creating Your Own Deionized Water
For users with ongoing, high-volume requirements, generating DI water on-site is the most cost-effective solution for securing a consistent supply. This method involves setting up a multi-stage water filtration system that combines reverse osmosis (RO) with a final deionization stage. The RO unit serves as the initial purifier, removing the vast majority of dissolved solids and protecting the final resin stage from rapid depletion.
Following the RO membrane, the water passes through a deionization cartridge, which contains mixed-bed ion exchange resins that effectively strip out the remaining trace ions. This combined RO/DI system reliably produces water with near-zero total dissolved solids (TDS). It is the standard for applications like saltwater aquariums or specific electronics cleaning. To monitor the system’s performance and ensure the DI resin is still active, a simple handheld TDS meter is necessary to test the water’s purity, confirming the reading is 0 parts per million before use.