i dealt with a lot of different customers at my summer job (restoring decks) and i've had situations like this come up pretty frequently. i try to tailor my response to the person asking the question. so if the person looks uninterested, stern, unhappy, etc. i try to keep it short, a simple "yes it really is" said playfully with maybe a bit of a chuckle keeps it short and the playful/upbeat tone makes it less likely to come off as rude. if they seem like nicer, more sympathetic people, i tend to add a bit more to it. i might throw in some kind of mishap that happened because of it (like "i forgot my raincoat" as suggested earlier) just to get a bit of a conversation. the problem with this is that i've gotten trapped in long conversations that i desperately wanted to end but didn't want to seem rude, watch out for the elderly, they've got more time on their hands and tend to be chattier.
now i didn't always get the impression that it went well, but there were a lot of calls to the office raving about the good jobs i did, despite being late, not finishing the job because of time conflicts, bad scheduling, etc. so i think i did pretty well with the conversation.
the main thing to remember is that they are essentially your customers so try to be upbeat with them, be polite and try to keep the conversation short so that you can get your job done more quickly and/or get more work done. most people (key word being MOST, not all) don't really want to be held up talking to the hired help for too long, so try not to let yourself talk their ear off.