I usually find worms in pots that have had yellow/brown water draining from them, whenever I repot them.

What is the potting mix/soil like (ingredients)?

Tiffany-Worms! I hope not. I don't mind them outdoors, but no worms inside please. How do they find your way into your pots?

I don't think worms are likely...it's in a small plastic cup with transparent sides and I haven't seen any wriggling around.

Rina-It's MG Seed Starter mix. I don't think it previously drained yellow water the last time I watered, but I could be wrong. I watered both times with Poland Spring water, watering until it drained.

I like to occasionally soak my plants' pots in water up to the soil line. I'll let them soak for roughly half an hour to an hour. When the water drains, it'll sometimes have this dirty brownish tinge to it. So I'll pour even more water thru the soil until it finally begins to run clear. This will flush away all of the dirty water, taking with it lots of the dissolved solids.

When the runoff coming from the pot looks like this, just keep running fresh water thru it until it begins to run clear, or mostly clear. Afterwards, just let it finish draining thru, before moving your plant(s) back to their usual spot. This gets more pronounced when you've just repotted something and the plant (s) haven't become established just yet, and the soil hasn't had time to settle. Many of my newly repotted plants are still doing this. I wouldn't worry about it.

Oh yeah, one more thing, don't reuse the dirty runoff water on other plants. Or you'll just be adding those dissolved solids to them instead. Always use fresh, clean water for all of your plants. :)

I think worms get in pots when pots are outside &/or from keeping bags of soil outside.

I thought that mix has some bark in it, or some compost. I have seen similar (even darker) runoff from a pot that was filled with partially decomposed bark and it was rained on for couple of days (one of those hanging pots that usually collect water since the drainage is raised). Perhaps lots of peat? - but you say this is first time that runoff is brownish? I don't know about fertilizer causing it, I would think that would take quite some time for salts to built up. How long are the plants in this soil?

It's been in the soil for about a month. I haven't fertilized since it was potted in to the soil.

Okay, so the next time I water I'll continue watering until it turns clear, if the yellow runoff appears again. Don't worry, there's no way I'll use dirty looking water on my dear plants ;)

Seems totally normal to me if its a peat mix.

Nothing to be concerned with as long as you flush regularly. And, if you flush regularly, you probably won't notice this.

As Al pointed out, the water is just stained from the peat.