Audi A6 2,5 TDI 1996 loosing water.....

i have just bought this nice car..... with 190.000 km on the clock
i drove i home from Berlin to denmark, with no water loose.
when i drive it normaly, ther is no whater loose......even after 200
km but when i drive hard, for only 20 km the goes to minium and the alarm sounds....
any idees??? what i got be??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.