Water leaking into car interior

After my Honda Civic was stolen and stripped last week, a friend gave me his 1994 Chevy Cavalier 2-dr 4-cyl manual transmission (167XXX miles) to tide me over while I looked for a new car. This Cavalier leaks water (into the floor of the front seat – up to a couple inches) in the rain. I’ve heard this is from water massing in the wheel wells – anyone know? Anyone solved this successfully? As a last resort, I’ll drill holes in the floor boards so it drains, but if the car is worth fixing, I’d rather do it right. Thanks!

Does it have a sun roof (should be called rain inlet device) If so it is likely that it has a blocked drain and cleaning out the drain will fix it.

Honestly, a Chevy Cavalier with 167,000 miles on it is not worth a lot of effort. Drill the holes in the floor where the water pools (be careful to drill where you will not impact anything else, such as your exhaust system) and focus on buying another car.

Just out of curiosity, does the car accumulate interior water while driving in the rain, or does it happen when the car is parked and rained on? Do the tires have good tread?
You mention the wheel wells as a possible explanation. Tires displace water to prevent hydroplaning in the rain. Good tires do a much better job of displacing water than old, worn out tires. When you drive in the rain, that water has to go somewhere. In heavy rain gallons of water will be displaced every few seconds. In most cases the water sprays out and away from the car. But if the wheel wells have serious body rot, especially toward the rear of the wells, and if the rot has created holes in the wheel wells, then certainly driving in heavy rains might result in an interior flood.

You can visually inspect the front wheel wells and even (carefully) feel around the wells (the rear of the wells) for rot and holes. If you find holes in the undercarriage then I think you have your answer.
Finally, the car is not a Honda Civic. It’s not even close. It is a nice little cheap car that a buyer can expect to get a 100,000 out of and that’s about it. Go find another Honda used.

This is a very common problem with GMs of this era. I have owned lots of cars that do this, but have never managed to figure out what causes it. My theory is that the HVAC box, which houses the heater core and a/c evaporator core, has gaskets that go bad or develop cracks. When it rains, water normally enters the box via the cowl inlet for fresh air and drains out through the drain plug. Unfortunately, the water will also end up inside the car via the bad gaskets or cracks in the plastic box. I have never investigated this theory because it would be a major pain in the butt and I have never had a car worth sinking that kind of time into to solve a problem this trivial. I just drill drain holes in the floor pans to drain the water out of the car. The carpet still gets wet, but my shoes and pants stay dry.