Water leaks When it rains my floor on both the driver and passenger become very wet. It leaks from some where under the car from the inside.

SOURCE: water in floorboard

Either the sealant that was used in putting your windshield in has began to fail, or there may be a larger opening under the vents, or on the firewall in the engine compartment. Look under the vent slats/holes under the windshield wipers. Look in the bulkhead that separates the engine from the dashboard(With the hood up). Those are the only ways water is getting in. Seal it with an expanding style sealer

SOURCE: Wet Headliner

You likely have a water leak around the 3rd brake light mounted on the top rear of the cab. I had this same issue on my 96 Ranger Supercab and found that the foam seal had gone bad and was allowing water to leak into the back of the headliner around the light fixture. It ended up soaking the headliner from one side to the other as the headliner acts as a 'wick'. You can repair this issue by either replacing the sealant around the 3rd brake light or replacing the brake light. There are two screws which secure the 3rd brake light assembly to the back of the cab. Remove these and it will pop right out. I upgraded mine to an LED light when I replaced it. That solved two issues at once as I'll never need to change a bulb there again. If you want to be cheaper you can not replace the light and just seal it with rubber silicone sealer.

SOURCE: leak

I was advised that i could pay $135+to take apart dash and find source of leak.I figured it out after it snows or rains real-hard then a gusher would happen when i stopped or started car. The solution is simple lift the hood ,and on the passengers side there is a retangular rubber plug that slowly releases water from the wiper reservior. it is above the exhaust manifold. be careful when you remove it because the vapor from the exhaust may steam-burn your hand.the dealer speculated it was a blocked air-conditoner drainage tube.but i removed it and leaves from the wiper resv. came pouring out. this cost me ZERO DOLLARS AND ZERO CENTS. we have had 2 major storms with no leaks....Texas Stang

SOURCE: 2001, rain water comes onto the passenger side

Are you sure it's rain water and not coolant? Coolant would have a distinct smell.

Does the car have a sunroof? The drainage tubes on sunroofs can get stopped up and allow water to enter the car.

SOURCE: water leaking inside 2001 ford focus passenger

The ford focus and Taurus models from this period are notorious for water leakage. Unfortunately it can be from two possible causes. Lets start with easiest first. The water dam (black plastic) where the windshied meets the hood (on outside) sometimes pulls away from glass allowing water to run into the crack and then into the dash and into primarily passenger side. The fix for this is listed in a TSB by Ford and the dealer can install, for a price ofcourse, a replacement damn that helps. For my sons Taurus to diagnose if this was the true problem we put a piece of clear packing tape over the place where the dam meets the windshield making sure it was sealed to glass tightly and then waited for next rain and it was dry so that fixed it. SECOND possible cause is a bad heater core. If the wetness smells sweet like radiator fluid or sugary sweet then this is probably a coroded heater core that leaks radiator fluid into the passenger compartment. It is located in center of dash closest to passenger side. Unfortunately if this is the case it needs to be replaced and a radiator shop will charge anywhere between 250 to 500 to do the job with part included. If it is the HEATER core you should check your coolant level regularly because it operates on pressure and with a leakign heater core you can lose pressure and possible have engine overheating. Good luck