Smelly water in cellar?

Hi, we have a problem with our cellar. When we have people living in the house next to us (rented) we get the most awful smelling water run through our cellar. We have a natural spring in the cellar, but the water from this is crystal clear. We have tried to get enviromental health to sort it and they are useless. We have figured it is cracked pipe as all of the drains have been checked. How do find out where the cracked pipe is without access into the house? The landlord of the rented house doesn't care.