I have water leaking into both drivers and passengers footwells in my Suzuki Grand Vitara. Heater matrix seems fine and the washer bottle pipes seem fine. Have checked seals on door panel. Again, fine. Have poured water down the windscreen which flowed out of its proper points - so not the problem either. Any other causes?

If it is inside the car in one footwell it will be one of three things. It will be either a leaking pipe to the rear windscreen washer jet, a worn door seal rubber or the heater matrix behind the dashboard.
Get into that footwell and using the back of your hand start at the floor and feel the carpet for wetness. Work your way up the carpet towards the underside of the dashboard. Your looking for the point where the carpet goes dry. Try this near the centre of the car and nearest the door. Floor only suggests washer pipe. Wet around the door is possibly a door rubber and high under the dash is most likely the heater matrix. This may seem an odd question but does the wetness have a smell? A rotten egg smell suggests screenwash. A sweet smell could be coolant.

Most likely problem is a leaking heater core. This is what usually causes water leaking into the passenger compartment. Quick fix on many vehicles is to get a hose adapter the same internal diameter as the heater hoses, remove the heater hoses from the firewall connection to the heater core, and install the adapter, making a bypass loop. This will allow operation of the vehicle without coolant loss until you can replace the heater core. Of course you will have no heat in the passenger compartment during this time.

heater core or hose connection leaking

double post. there are no drains. read one post back
in doors yes, in body no.

Yes. It could cause the water to seep into the passenger compartment thru seams in the sheetmetal or the heater box instead of draining onto the ground.

She's rusted in the floor pan/ wheel well area--contact body repair or sell/ junk it.

heater core is leaking

Could be the door selas or grommets at the firewall or drains if you have a/c or moonroof.

Yes, the plastic caps at the bottom of the footwell, are for drainage. (Don't forget to replace them. You may not be pleased with yourself, if you don't, on a real rainy day!)

Does the water have a real nasty smell, and the inner windshield has a film on the inside? If so, then you have a heater core leak, and it's antifreeze.

If not, your air conditioning drain duct is plugged, and needs to be cleaned out. I also suggest a real weak solution of bleach and water, to be applied in this area, to kill any mildew that might form. (Unless you are allergic to bleach. If so, you may want to try an alternative. Mildew is bad for your respiratory system)

are you sure it's the washer bottle sounds like the heater core is gone if window is fogging up it's the heater core