DMSO is often sold pure (approx. 99.9% purity). If it is stored for a longer period of time, it can also attract moisture and thus water. Normally we only know ways to dilute something. To concentrate liquids again higher, we know actually only by boiling. We cannot use this here with DMSO because it would destroy the chemical structure. But we can easily take advantage of one property of DMSO. DMSO becomes crystalline below 18 degrees and thus solid, especially if it is delivered in winter months. If we now place the DMSO bottle in the refrigerator overnight, the DMSO inside will solidify, but the water will not yet freeze at refrigerator temperatures and will settle on top. Now we simply pour off the separated water and close the bottle again. Then we heat the DMSO bottle in a warm water bath (no microwave!). By this simple procedure we have increased the concentration of DMSO back to almost 100%.