What is Type 1 Water?

What is Type 1 Water?

What does type 1 water mean?

Reagent water has quantitative specifications that describe the level of purity for the water.  These specifications have been described by ASTM (American Socity for Testing and Materials) D1193, ISO (International Organization for Standardization) 3696, and CLSI®-CLRW. (Clinical and Laboratory Standards Institute-Clinical Laboratory Reagent Water). The most commonly used standards, ASTM D1193-6, are summarized in the tables below.

ASTM Standards for Reagent Water
Measurement (Unit) Type I Type II Type III
Resistivity (MΩ -cm) at 25° C >18 >1 >4
Total Organic Carbon (ppb) <50 <50 <200
Sodium (ppb) <1 <5 <10
Chloride (ppb) <1 <5 <10
Total Silica (ppb) <3 <3 <500

The ASTM standards are further subdivided into A, B, and C.

These standards can be used in conjunction with the Type of water.

ASTM Standards for Reagent Water
Measurement (Unit) A B C
Heterotrophic Bacteria Count (CFU/ml) 10/1000 10/100 1000/10
Endotoxin (units per ml) 0.03 0.25 n/a

Here are some additional definitions of the parameters they use to indication the water's purity.

Resistivity - the tendency of water without ions to resist conducting electricity.

The unit of measure is megohm-centimeter (MΩ-cm), often shortened to MΩ or "meg".  It is generally used for high purity water.  The theoretical maximum is 18.2 MΩ-cm at 25°C. The higher the ionic content - the lower teh resistivity and the lower the ionic content - the higher the resistivity (high resistivity is good!).  In ultrapure water systems this value is determined using an in-line meter.  Conductivity and resistivity measurements are inversely related to each other.

Conductivity - the tendency of water that contains ions to conduct electricity.

The unit of measure is  microsiemens/centimeter (µS/cm) or microhm/cm. The measurement is used to measure feed water or lower quality treated water.  The more ions present in the water, the higher the conductivity.  This is measured by a conductivity meter.

Total Organic Carbon TOC - a measure of the organic contaminants found in water.

The measure is parts per million (ppm) or parts per billion (ppb).  Feed water can be in the 2-5 ppm range and the best high purity water should be in the 1-5 ppb range.  Measurement of TOC is done using an in-line system.

Conductivity and Resistivity

Electrical conductance or resistance is measured by two in-line eletrodes.  Electrical current moves through water using ionic molecules as stepping stones.  The fewer stepping stones, the more difficult the passage of electricity.  This causes less electrical conductance and more electrical resistance.  The temperature of the water also affects the conductivity/resistivity so readings are usally normalized to 25°C via temperature compensation.

We use resistivity to measure ion concentration in pure water.  We undersstand water and realize that in order to achieve Type 1 water, meeting the most stringent requirement of our customer, multiple technologies must be used.

Total Organic Carbon (TOC) Analyzer

Our patented TOC analyzer monitors TOC and resistivity, so you can be sure that the product water exceeds the most stringent requirements of analytical or biological applications.  To ensure accurate measurement of product water quality before it is dispensed from the system, the TOC analyzer is positioned after all purification technologies, next to the resistivity cell.

Watch this Water System Video

Information courtesy of Thermo Scientific

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