A recording head filling liquid contains a specific moisturizing agent, a monovalent alkali, and water. The specific moisturizing agent is a compound represented by general formula (1) below. The specific moisturizing agent has a percentage content of at least 19.00% by mass and no greater than 42.00% by mass. The recording head filling liquid has a static surface tension at 25° C. of at least 20.0 mN/m and no greater than 29.0 mN/m. In general formula (1), a, b, and c each represent, independently of one another, an integer of at least 1 and a+b+c is at least 4 and no greater than 20.