The 10 O'Clock Dairy owner Ge Song said his store in Prince Albert Rd, Dunedin, had been the scene of five attempted robberies since he bought it four years ago.
But thanks to the large "super-soaker" water gun and a large stick under his counter, he had never had to give money to would-be robbers.
Mr Song said he did not have time to use the water gun on Monday night, but he had done so to several previous attempted robbers, soaking them.
"They no say anything. I just wet them and they run.
"I sad I no get to use my water [gun on Monday night]."
Mr Song said he had been threatened at the store many times in recent years, and when a man entered his store on Monday night with a knife, demanding money, he laughed as he sounded an alarm in the shop and told the man to leave.
The man ran, but had he stayed a moment longer, he would have been soaked to the skin.
Mr Song said he refused to be intimidated by people threatening to rob his store.
Two men were arrested on Monday night for their alleged part in the attempted robbery, after a member of the public saw a man leave the store and climb into a van.
The witness followed the van and contacted Dunedin police.
Last night, police arrested a third man, a 19-year-old cleaner, and charged him with aggravated robbery for his alleged role in the incident.
He also faces charges related to robberies at the Mornington BP service station on June 5 and Green Island Post and Paper two days later.
He is expected to appear in the Dunedin District Court today.
Detective Sergeant Rob Hanna, of the Dunedin CIB, said police were not ruling out the possibility of further arrests.
• A 19-year-old unemployed man and a 21-year-old labourer received a registrar's adjournment yesterday on an indictably-laid charge of attempting to rob a male while armed with an offensive weapon.
They have interim name suppression and were remanded on bail to June 28.
