Question about rehab

Hey. I'm sorry if this is the wrong place, but I have a Tennant that has an issue with alcohol.

He recently went through rehab, and I was told he was trying to stay sober. I don't have an issue with alcohol myself and I have no idea what it's like.

Today I came home from walking my dog and he's having a drink at 10 a.m.

He's tried to convince me that rehab says it's okay to still have one once in a while as long as he's in control which I'm not sure I believe.

He's not out on control, but I believe he's been intoxicated a few times.

Can anybody tell me what goes on in rehab? Like do they encourage 100% sobriety?