Roof Water
Can downspouts be connected to the footing drain?
No. A footing drain exists to relieve groundwater pressure at the foundation. Feeding roof volume into it works against that purpose and can push water toward the structure during exactly the storms when the footing drain is most needed. They should remain separate systems with separate outfalls.
In more detail
This is one of the more damaging shortcuts in residential drainage because it is invisible once backfilled and the failure it produces looks like a foundation problem rather than a plumbing one.
A footing drain is sized to relieve slow groundwater pressure. Roof discharge during an intense storm arrives as a large volume in a short time — enough to pressurise the system and force water along the path of least resistance, which is the foundation wall.
If you have an existing tie-in of this kind, separating them is usually straightforward and is worth doing before adding any further drainage.
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