I'm a licensed contractor and I'll try to give you the short of it. You can repair or I think even install (varies by city) as long as you stay under a certain dollar amount (I think it's $2k) of annual revenue per site. In other words if you have a customer that spends $2k a year with you total (not just irrigation) you can't do irrigation work for them w/o the license. If you have a customer that you do $500 a year you you can do irrigation work for them up until the $1500 mark. This is the way I remember it being explained to me. If you're in a bigger market it'd be best for you to go ahead and get the license.