Water used in a lab can in general be classified as tap-water,
deionized water (dH20) or distilled/deionized
1. Tap water is most frequently used for cleaning. For making media and
solutions dH20 and ddH20
are frequently used. Special applications such as HPLC my require higher
2. Deionized water (dH20) is obtained by a
filtration system (e.g. Milli-Q (Millipore) ). The system removes
ions and organic materials. The purify of the dH20
produced is measured by resistivity (which measures residue ion concentrations)
and total organic carbon (TOC). A system may have built-in resistivity
and TOC monitors. Users should pay attention to these monitors to recognize
failure of the deionization system.
3. Filters for the filtration system should be checked regularly and changed if
4. UV photo-oxidation is available for some systems, which further reduces TOC
to produce "HPLC-grade" water.
5. Deionized water (dH20) can be further distilled to