It seems that in every movie I see that during night scenes, the roads look like they were washed down recently. In the story, it hasn't rained so there is no reason for it to be wet. The same thing in TV shows. Why do they do this? Is it something to do with how it looks on film? I am sure I have seen a very few that didn't have it washed down and it didn't look bad so why purposly make an 'error' in the story?

It's conventional wisdom that wet streets look better on film. Personally, I hate it.

Yeah, it probably reflects light better too.

lighting.

John Frankenheimer had an interesting comment on this on the Ronin commentary. They intentionally wet the streets and cars for a scene since they were shooting it over several nights. It would rain some nights and not others so to retain continuity between shots, they went with wet.

Dont they usually wet the roads down in order to get cars to make sharp u-turns and stuff?

Wet roads reflect the light.

For a great look at dry roads, check out Dazed and Confused(and I'd gather most indies shooting night shots)

...for the same reason the cars driving on them don't have rear view mirrors.

For that nice WHOOSH! sound as cars drive by....

Yup, it's all about lighting. I spent the better part of the month of July on a movie set (see here) and they basically bring in fire trucks to hose down the streets and sidewalks.

Don't get me started about all the missing headrests...

Maybe to justify or tie in with those ominous rumbles of thunder they play during every tense scene or conversation.

In the commentary on Election, the director talks about this. Specifically that he hates it.

Why is this a hated practice? I mean, who really cares if the street is wet?

Personally, I don't care (I think that it makes night scenes more visually appealing). I suppose it does take away the believability of some scenes though. For example, if there is a street drenched with water in oh, say Death Valley perhaps.

I recall when David Lynch made Lost Highway, there was a scene where it had rained and the pavement was all wet, and there was a loss of continuity with his shots. So he gave a couple people a hose to play around with in the background so people could connect the wet pavement with them.

So, is it just for lighting or for continuity in situations were it might rain one time and not on another day of shooting?

i personally think its for continuity, if you are shooting a scene all night, and say it starts raining at 2 am, and you have already been shooting since 10 pm, when editing, some shots won't match up (and many times the budget isn't big enough to afford to re shoot it.

Another question on the night driving topic. In every movie I have ever seen that has a car pull up at night and the actor gets out they leave the lights on. Every damn time! It just gets to me.