A broken hosepipe blew the whistle on a large indoor marijuana farm in the Villafranqueza area of Alicante.
An Alicante Policia Local patrol spotted water pouring out of the first floor of the building.
Nobody answered the front door and firefighters were called to gain access and find the source of the leak.
The entrance had been blocked by a set of plasterboards.
A fire crew used a ladder to get in through a first-floor balcony window.
They spotted an array of bright lights and were immediately hit by a strong smell of marijuana.
The water was pouring out of an illegally connected hose pipe used to irrigate the marijuana plants.
Police and firefighters discovered several dozen plants and cables hooked up to illegally use the electricity supply to power up the lights.
The Policia Nacional are leading the investigation into the indoor farm which includes trying to track down the property owner.