When Jake goes to investigate the Northwest Valley, and see if the water department's really irrigating orange groves out there, he finds his worst suspicions confirmed. As he drives down a road into one of the orange groves, a group of farmers fire guns at him until they stop his car.
When Jake confronts him, an older angry farmer accuses him of being someone from the water department. It turns out that the water department hasn't been helping them at all. In fact, men from the water department have been sabotaging their farms. As the farmer himself tells it:
FARMER: The water department's been sending you people to blow up my water tanks! They threw poison down three of my wells! I call that a funny way to irrigate—who'd hire you for a thing like that?
Thanks to this info, Jake's confirmed that the water company's cover story is definitely wrong. Someone really is stealing the water. He already knows this, having seen the water being diverted away from the reservoirs, but it's nice to prove it.
Also, the famous director Ron Howard's dad (Rance Howard) plays another angry farmer who jeers Hollis Mulwray at a town hall meeting, accusing Mulwray of working against the farmers—which turns out to be totally false. Trust Richie Cunningham's dad to get things totally backwards.