# diH2O, dH2O, and DI H2O. What do they mean?

What do $\ce{diH_2O, dH_2O}$, and $\ce{DI H_2O}$ mean?

I'm not asking for a description of deionized water and distilled water. I'm asking what the three abbreviations/formulas mean.

In other words, I'm asking someone to fill in the blanks below.

• $\ce{diH_2O = \_\_\_\_\_}$
• $\ce{dH_2O = \_\_\_\_\_}$
• $\ce{DI H_2O = \_\_\_\_\_}$
• * diH2O = deionized water * dH2O = distilled water * DI H2O = deionized water – Curt F. Feb 17 '16 at 5:01
• Thanks @CurtF. I found a book that referred to diH2O as distilled, not deionized water. Is there no commonly accepted standard, or is this just a fluke reference I found? books.google.com/… – kdauria Feb 17 '16 at 5:06
• I don't think there is a commonly accepted standard. If I had to guess, I'd say more often than not di$\ce{H2O}$ is used to mean deionized water, but I've nothing but my own experience to base that on. Sorry for the lack of references. Also, ddH2O is a common abbreviation that used to mean "double-distilled water" but now is used to refer to highly pure water produced by laboratory purification systems such as those from milliQ or similar. – Curt F. Feb 17 '16 at 5:11
• As Curt F. indicates, what they stand for and what they are in practice are two different things. In practice, the four abbreviations "mean" the same thing: high purity water. If there's some practical difference between distilled, double-distilled and deionized water that means one is suitable and the other is not, you'll normally get a more extensive description of the minimal performance and purity characteristics necessary for the application. – R.M. Sep 26 '16 at 16:21
• A meta discussion about the edits to this question can be found here: meta.chemistry.stackexchange.com/q/3467/7951 – Loong Dec 3 '16 at 1:36

I don't think there is a commonly accepted standard. If I had to guess, I'd say more often than not $\mathrm{di}\ce{H2O}$ is used to mean deionized water, but I've nothing but my own experience to base that on. Sorry for the lack of references. Also, $\mathrm{dd}\ce{H2O}$ is a common abbreviation that used to mean "double-distilled water" but now is used to refer to highly pure water produced by laboratory purification systems such as those from Milli-Q or similar.
• $\mathrm{DI}\ce{H2O}$ = deionized water
• $\mathrm{di}\ce{H2O}$ = deionized water
• Such water is often available from centralized water purification systems in buildings that host many chemical laboratories. It isn't as pure as "$\mathrm{dd}\ce{H2O}$" (see below) but is subtanstially more pure than tap water.
• $\mathrm{d}\ce{H2O}$ = distilled water
• $\mathrm{dd}\ce{H2O}$ = doubly distilled water
• $\mathrm{mq}\ce{H2O}$ = Milli-Q water
• The brand name of a popular type of water purifier that gives purity similar to $\mathrm{dd}\ce{H2O}$