I have alto 2004 model, same problem happened with me, water was getting reduced from radiator about 2 glass every day after riding 40 km. Head gaskit was okay as the mechanic checked by removing radiator cap and giving race, there was no bubbling of water from radiator. Hose pipes were okay and there was no leakage from hose pipes. I serviced radiator and it was working fine. Then I went to jameel autos khudadad colony stop, and showed my car to irshad bhai, he checked the car thoroughly and found that flange was rusted and water was being evaporated thus getting reduced. He changed the flange with a new one and after date proble was solved, car didnt reduce water at all from radiator and water was being sucked from bottle and sometimes I have to fill water in resorvoir bottle. I would strongly suggest you to go to irshad mechanic at jameel autos, he is competent mechanic. Hope this helps you.