I am sorry that your question was unanswered for long.
A salivary gland inflammation needs to be considered for increased foamy saliva and foamy tongue as irritable gland do secrete excess saliva. Your primary care physician can examine or palpate all three major salivary gland; namely parotid, submandibular and submental. Herbs too can be responsible for the irritation of the salivary gland resulting in increased production of the saliva (if you are using any). But many times it subsides spontaneously and no cause is found. Read about the excessive saliva in this authentic resource;
Consideration of the gastroesophageal reflux disease (GERD) should also be done for excess water in mouth. Sleep disorders, anxiety and emotional disorders also are considered for cause of excess water in mouth. Read about the GERD symptoms;
Increased foamy saliva and grey tongue can be caused by the gastroesophageal reflux disease (GERD) and hiatal hernia. Following measures can help;
1) antacids; Maalox
2) acid blocker; Prilosec
3) loosing weight, if overweight.
4) avoiding alcohol, citrus fruits and juices, chocolate, and tomato based products
5) avoiding large meals. Eat 5 small meals in a day.
6) wait three hours after the meal before you sleep.
7) elevate head end of the bed by 8 inches.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.