Case in point, our sad dirty sink...
Not very shiny is it? Well let's take an even closer look shall we?
Yucky isn't it? Well the fastest and "greenest" ways to get rid of all that hard water buildup is some warm vinegar. Yep, just plain old vinegar.
I like to heat the vinegar up in the microwave for about 30 seconds (doesn't make for the best smell in the world but it does help degrease the microwave). Once the vinegar is heated I pour it into a spray bottle and spray the heck out of the sink. You could also go the route of dabbing a wash cloth into the bowl of warm vinegar (just be sure the vinegar isn't scalding hot, got to use common sense now people). I like the spray bottle version because I can do something else for about 10 minutes (like play Candy Crush), let the vinegar do it's job then come back and wipe with a wash cloth.
If you have a couple of stubborn spots, like I did, you can up the cleaning power by adding a couple dashes of baking soda. It works wonders when combined with vinegar.
Now for the after!