A standard competitive water polo team has seven players in the water, including one goalkeeper.
That normally means six field players and one goalkeeper. The goalkeeper wears a distinctive cap, usually red, and has special privileges near the team's goal, including being able to use both hands within the goalkeeper's designated area.
Seven is the number playing at one time, not necessarily the full team roster. Competitive teams carry substitutes, and players can be replaced during permitted stoppages or through the substitution area. Modern international rules have changed roster limits in some competitions, but the traditional in-water lineup remains seven.
Water polo is played between two teams in a pool, with players swimming continuously while passing and shooting a buoyant ball. A team may temporarily lose a field player after an exclusion foul, creating a power play, but its normal starting formation still contains six field players and a goalkeeper.