Hi.. Welcome to HEALTHCARE MAGIC. I have gone through your query and can understand your concern.. As per your query in case if you have started a new diet and you are taking more of fibres in diet and as you have increased more of physical activity in the form of workout then it is clear that your requirement of water intake is increased as the excretion from body in the form of sweat has also increased and you are getting dehydrated leading to dry mouth.. Also taking 2 litres of water is not at all enough and you should take atleast 3 to 4 litres of water daily.. You can also chew sugar free chewing gums as it helps in stimulating saliva flow and relieve dry mouth.. In case if you do not see improvement in 15 days consult an Oral Physician and he can evaluate you for other causes of dry mouth like salivary gland disorders, oral infections like thrush, side effect of medicines, hormonal changes, diabetes etc and treat you accordingly.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.