Konosuba: Even More Explosions on This Wonderful World! Vol 4

From the Yen Press edition

At Cecily’s request, Megumin and her friends set out for the hot spring town of Arcanletia, where out-of-control slimes (totally not Cecily’s...) have wrecked all the plumbing! To uncover the truth behind the slimy fiasco, they head straight to the source of the water. But what they find there is unthinkable...!

Source: Yen Press