I have a 2006 chrysler grand voyager 2.8 crd and i seem to be losing water the header tank is not totally empty but every couple of days i have to top up for the last week now i have noticed a warning light on the dash comes on then goes out it turns out to be water in fuel filter warning does anyone have any idea on this

 

If it's like my 2.5, the fuel filters near the fuel tank underneath and has a thing you can turn to drain water off.
Take a little out via that (not too much or you may empty the filter and struggle to restart car)and hopefully it'll stop the water in fuel light.

As far as the water loss goes, it could be lots of things from head gasket (water in the oil? bubbles on the dipstick? Oil has the appearance of mayonaise?) To a leaking radiator or coolant pipe and probably more in between.

If the oils ok, once the cars had a good run, open the bonnet and have a good look everywhere for evidence of leaking water. Check round the radiator and follow all the pipes/hoses to and from it. Also check for dampness in the footwells (I'm assuming the heater matrix would leak in here like in other cars I've had but not sure).

Good luck.