Is this the first time in a year that you've seen moisture there? Has it been raining an unusual amount there lately? Do you have gutters on the house and are you sure they are clear and allowing water to flow away from the house properly?

You have three choices for basement water:

1) plumbing leak - obviously not

2) condensation - even if your walls were condensing water, it wouldn't form a near-perfect 2" strip at the base if it could muster up enough accumulation prior to evaporation to run down the wall.

3) groundwater intrusion - you may have a high water table, which can be permanent or temporary with heavy rains. If water is sitting right below the slab, it can work its way via capillary action to the gap between the foundation wall and edge of slab, "soaking" into the concrete on it's edge where you can see it. Using perforations in your sump pit crock can alleviate under-slab water.

Thank you.

Yes it's the first time I saw it after moving in last year. I have no gutter. We had the heaviest snow (like only 2'') this winter last week. I did notice water puddles right underneath my roof when the snow melt. Does that suggest that soil is soaked? A colleague of mine suggested it might be cove joint seepage. Does it seem a probable cause?

" I did notice water puddles right underneath my roof when the snow melt. Does that suggest that soil is soaked? "

I do not know about soaked but that would definitely sound like the cause. Why no gutters?

What I was saying about water under the slab will come up between the gaps - you are referring to "cove joint seepage." That would be a water table, which is a "solid layer" of water under your house and is always present - it's a matter of what elevation the water table resides. This can fluctuate with seasons and amount of rain/snowmelt that occurs. Again, your sump pit crock (the "tub") will have perforations (if steel, tabs you bend open, if plastic, holes you drill) that will allow water from under the slab to enter the crock (separately from your piped footing draintile system), and be pumped out by the sump pump.

I'm afraid my basement doesn't have a drainage or sump pump inside. So if water starts accumulates, shall I install something like a perimeter drain and a sump pump?

What I find interesting is that the moisture seeps through "the floor and the wall", but not along the slab joints.

Not having a sump pump, footing drain tile, or even a pit waiting for a future sump pump is not the norm in a recently built basement, let alone against code to not have footing drain tile. Double check you don't have a pit somewhere.

If underslab water is a problem, it is a very big expensive job to sawcut the perimeter to intall an interior drain system. It is often more expensive to dig outside, which is the best method, to install an exterior footing drain tile system.

There is probably a vapor barrier of polyethylene plastic under the slab, which minimizes some water, but it will still get to under the slab. The slab is 4" thick. The control joints are sawcut to force any possible cracks to follow the sawcut lines - that doesn't mean that the slab has actually cracked to allow water through.