Do I make a Brachah on water during a meal?
Bread is considered a halachic staple on which we are kove’a seudah (establish a meal). Most foods are included in the original brachah of Hamotzie as they are considered dvarim haba’im machamas haseudah (foodstuff that comes [to be consumed] on account of the meal)—they are therefore tafel (secondary) to the bread as meal accompaniments. The halachic consensus is that we also do not make a brachah while drinking water during the meal, since our thirst is b'sibas hapas (caused by [eating] the bread or meal) and therefore tafel to the bread.* (Wine is not tafel, as well as other hard drink in certain circumstances—see Halachah #197.)
The water we drink during the meal is only considered tafel if it is indeed b’sibas hapas. This is not the case in situations where the thirst originates from other sources, even when drunk during the meal. If an individual was thirsty before washing for bread, but did not have access to water—as a guest or when rushing to arrive at an event on time—and only drinks once settling down to eat the meal when water becomes available, they are required to make a brachah. The same would apply to a sweaty dancer at a simchah (happy event, e.g. a bar mitzvah or wedding) who visits the refreshment table for a revitalizing thirst-quencher some time after having eaten the last of their bread. In circumstances where drinking is completely unrelated to eating the meal, a brachah of Shehakol must be said.
(There is the additional issue of continuing to eat and drink once all remnants of bread have been removed from the table—which is a separate halachic discussion.)
However, a minority of poskim maintain that we should make a brachah on water or other drinks during a meal regardless of whether it is b'sibas hapas or for other reasons. Some are scrupulous to account for this difference of opinion; before washing, they recite Shehakol on a small amount of water—less than a shiur ([minimum requisite] amount needed [to recite an after-brachah]—see Halachah #73)—to include all drinking during the meal. In this case, all drinking is considered to be part of the original brachah, except in situations where there is shinui makom (changing [or temporarily leaving] a location—see Halachah #332 and Halachah #713). #814
*Other (non-alcoholic) drinks are also tafel, since they are drunk when thirsty and thirst usually comes as a result of eating. Even drinks which are not made to quench thirst are considered b’sibas hapas and are exempt from a separate brachah, as it is common to drink them after eating.