"I was in quite a tight confined space and ended up punching a hole in my knee with an industrial waterblaster.
"As the afternoon went on, the pain started increasing. I think I would have pumped 150ml of water into my leg."
The waterblaster was 3500 psi, he said.
The wound continued to weep with the pain increasing so he took himself to Accident & HealthCare on 2nd Ave where an X-ray found there was a large build-up of air underneath the knee cap and shin.
He was admitted to hospital by 11pm Monday.
"I woke up the next morning and who should be across the aisle from me than Blair who I had winched into the helicopter two weeks prior."
Blair Anderson was admitted to hospital after he severely broke his leg in a raft incident about two weeks ago.
"I recognised his face straight away because when I was winching him up from Wairoa River, he had this massive smile on his face.
"It was quite a severe break but he had this big massive grin on his face.
"We were both hobbling around on crutches together but everybody is giving me a bit of stick on how I could waterblast my own knee," Mr Campbell said.
Both men had injured their left knees, he said.
Mr Campbell said he later realised Mr Anderson was also his son's summer employer at Waimarino Adventure Park.
Mr Campbell was discharged from hospital on Wednesday while Mr Anderson was discharged on Friday.