leak in(to something)
Of a liquid or gel, to enter in(to something) by slowly seeping or flowing. I thought I had completely fixed the roof, but water still leaks in when it rains. There must have been a crack in the bottle, because nearly all the shampoo had leaked into my bag by the time I got home. The pool of fluid eventually leaked into the floorboards, causing them to warp and rot.
leak in (to something)
[for a fluid] to work its way into something. Some of the soapy water leaked into the soil. The rainwater is leaking in!