Drill or cutting oil is a product composed of water and oils that is used as a lubricant and coolant in parts manufacturing processes.[1]​ Its use is very common in machining by chip removal of metal parts and, to a lesser extent, in the transformation of glass.[2]​ For the machining of composite materials, because conventional drills could chemically attack the material[3]​, fluids developed specifically for this type of materials are used and that fulfill the same lubricating and cooling function.[4][5]​.

It usually circulates through a cooling and lubrication circuit that pumps the liquid over the edge of the tool to avoid excessive heating that could quickly deteriorate it.

Coolant improves the physical and chemical conditions of the contact area between metals, extending the life of the tools and reducing friction. It also carries out cooling tasks, preventing overheating of the tools and the parts on which they operate. Other effects are the evacuation of chips and filings, rust prevention and its cleaning effect.[2]​.

In its composition there are sulfur additives, paraffins, chlorines and also synthetic oils (polyglycols and esters). It is also common to add solid lubricants such as graphite, molybdenum disulfide and zinc disulfide").[6]​.

According to its composition and characteristics, the product is classified as synthetic, semi-synthetic") and oil emulsion derivatives. The most used are formulas based on mineral oil.[6]​.

The machine tools that usually use coolant are the lathe, the band saw, the milling machine and the drill.

In these machines, the coolant is in a tank from which it is pumped to its point of application (between the part being acted upon and the moving part of the machine), from where it is recirculated back to the tank. During this process, a good part of the product is lost; part of it evaporates, another is spilled and another is lost with the chips generated.[2]​.

When, due to continued use, coolants lose their properties and suffer alterations in their characteristics, they become dangerous waste that, as such, must be properly managed by the user company. Discharges into drainage systems cause serious damage to the environment, and can cause disasters among fish fauna due to their toxicity. Therefore, authorized waste managers must eliminate them.[2]​.

Various techniques are used for its destruction:[2]​.