thumb|Olympic Aquatic Centre at the 2004 Summer Olympics
Water polo at the 2004 Summer Olympics took place at the Olympic Aquatic Centre where women competed for only the second time in the event at the Summer Olympics.
Twelve teams competed in the men's event, where Russia was trying to avenge their defeat by Hungary at the Sydney Olympics. There were eight teams in the women's event, where holders Australia were hoping to retain the title.
Qualification
{|class="wikitable sortable" width=370 style="text-align:center; font-size:90%"
|-
! Nation ||Men's ||Women's ||width=55|Athletes
|-
|style="text-align:left;" | || || ||26
|-
|style="text-align:left;" | || || ||13
|-
|style="text-align:left;" | || || ||13
|-
|style="text-align:left;" | || || ||13
|-
|style="text-align:left;" | || || ||26
|-
|style="text-align:left;" | || || ||26
|-
|style="text-align:left;" | || || ||26
|-
|style="text-align:left;" | || || ||26
|-
|style="text-align:left;" | || || ||26
|-
|style="text-align:left;" | || || ||13
|-
|style="text-align:left;" | || || ||13
|-
|style="text-align:left;" | || || ||26
|-
!Total: 16 NOCs !! 12 !! 8 !! 260
|}
Men`s
{| class="wikitable"
!Water Polo Men
!Date
!Host
!Vacancies
!Qualified
|-
|Host nation
|5 September 1997
| Laussane
| align="center" |1
|
|-
|2003 World League
|27 June-24 August 2003
|Various
| align="center" |1
|
|-
| rowspan="3" |2003 FINA World Championships
| rowspan="3" |14-26 July 2003
| rowspan="3" | Barcelona
| rowspan="3" align="center" |3
|
|-
|
|-
|
|-
|2003 Pan American Games
|2-10 August 2003
| Santo Domingo
| align="center" |1
| United States
|-
|Asian Qualification Tournament
|22-24 September 2003
| Almaty
| align="center" |1
|
|-
|African Qualification Tournament
|
|
| align="center" |1
|
|-
|Oceania Qualification Tournament
|
|
| align="center" |1
| Australia
|-
| rowspan="3" |Olympic Qualification Tournament
| rowspan="3" |25 January - 1 February
| rowspan="3" | Rio de Janeiro
| rowspan="3" align="center" |3
|
|-
|
|-
|
|-
!TOTAL
! colspan="2" |
!12
!
|}
Women`s
{| class="wikitable"
!Water Polo Women
!Date
!Host
!Vacancies
!Qualified
|-
|Host nation
|5 September 1997
| Laussane
| align="center" |1
|
|-
|Asian Qualification Tournament
|22-24 September 2003
| Almaty
| align="center" |1
|
|-
|2003 Pan American Games
|2-10 August 2003
| Santo Domingo
| align="center" |1
| United States
|-
|Oceanian Qualification Tournament
|
|
| align="center" |1
|
|-
|rowspan=4|Olympic Qualification Tournament
|rowspan=4|23-29 February 2004
|rowspan=4| Imperia
|rowspan=4 align="center" |4
|
|-
|
|-
|
|-
| *
|-
!TOTAL !! !! !! 8 !!
|}
- Canada took the place of the African team.
Medalists
Men's
{| class="wikitable" style="font-size:95%; text-align:center;"
!style="width: 15em" style="background-color:gold"|Gold
!style="width: 15em" style="background-color:silver"|Silver
!style="width: 15em" style="background-color:#CC9966"|Bronze
|- valign="top"
|