I don't believe I can asnwer your question difinitively but on the whole I don't believe one should be necessary. The real issue is, how far underground is the storm sewer relative to the basement floor. And, how absorbant is the soil plus what severe rainfall might be received?

Where we reside, we have both ejector pits and sump pits. Sanitary sewers are elevated above the basement floor level and any waste water produced in the basement must be pumped into the sewer. This is the ejector.

Groundwater is collected from around the outside foundation and emptied into a sump pit located in a corner of the basement. This water is pumped outside onto the lawn. I suspect it is this water which your builder says will not be an issue. Our soil here is primarily clay so will not retain much groundwater.

Hope that helps but don't be afraid to speak with your community permit department for their input.

Thanks fnmroberts

Great info....

Put it a sump pit and piping system anyway - here's why. Even if you don't need it for water, you may need it for radon mitigation down the road 8-12" of clean gravel under your slab, with a grid of inexpensive schedule 30 drain tile tied to a 36" deep sump pit makes an excellent radon mitigation system, as well as a way to get rid of any ground water. You replace the cover with a gasketed cover connected to the radon stand pipe and fan. In terms of moisture control - get the water away from your foundation to begin with - cut it off with a french drain so it never reaches the foundation wall and you'll have a much nicer home. Good luck.

I agree with DRKRUNK. I'd take the belt and suspenders approach. Sump pump, ejector pit, and you have to consider rain runoff, as well, with gutters, and downspouts directed away from the foundation, and waterproofing the foundation. Not the black tar stuff, some kind of fabric/dimpled product. Save yourself headaches/heartaches "I wish I had done that" regret.