A 2011 article in the journal Clinical Lactation (Mohrbacher, Nancy. The Magic Number and Long-Term Milk Production, Vol 2-1, 15-18) explains the physiology behind breast milk production, which is dependent on breast fullness and breast storage capacity.
Full breasts make milk slower. You want to nurse (or express) before your breasts are full.
Drained breasts make milk faster. Encourage baby to nurse fully, or express what's left to empty the breast more throughly.
The amount of milk that can be stored by the breast is not related to breast size but rather to the amount of room in the milk-making glands. Capacity affects how long it takes for the breast to become full. A woman with larger capacity can go longer between feedings without cuasing milk production to slow.
Mother needs to find the magic number of milk removals needed to keep milk production stable - an issue especially for mothers who are expressing. The number of breastfeedings per day should be fairly stable for the first 6 months, reducing as solid foods are introduced. 8 times per day is average; an individual mother's number may be more or less than this depending on her capacity.
The myth of Increased Fluids
While one should certainly avoid dehydration, studies like this one from 1985 ( Dusdieker et al, Effect of Supplemental Fluids on Human Milk Production, Journal of Pediatrics) demonstrate that increasing fluid intake does not affect breast milk production.