PURPOSE: The viscosity of mud water produced by dissolving a vegetable mucous substance and an additive in water in controlled by controlling the pH of the mud water. The process prevents the excessive flow out of the mud water, facilitates the excavation of earth, simplifies the method for the recovery and reuse of the mud water and enables the boring of a subterranean hole.

CONSTITUTION: (A) One or more vegetable mucous substances (e.g. guar gum) are dissolved in water, and the solution is added with (B) an additive such as borax, boric acid, etc., to obtain mud water. The viscosity of the mud water is controlled to a level suitable for the boring of earth by controlling the hydrogen ion concentration of the mud water.