An adjustable drip pan designed to be installed into tightly-enclosed spaces. Specifically, an adjustable drip pan comprising a bottom pan, said bottom pan comprising a bottom floor, a reservoir, and one or more walls; and a top pan, said top pan comprising a top floor and a lip, wherein said one or more walls form a ridge. Said ridge, said bottom floor, and said reservoir create a water-impermeable basin for collecting water, and said bottom pan and said top pan are slidably adjustable in a plane along an axis, where adjustment of said bottom pan and said top pan is limited, in a first direction of said axis, by touching of said lip and said ridge, and in a second direction of said axis, by touching of a first one of said one or more walls all and said top pan.