Aquatics at the 1985 Southeast Asian Games included swimming, diving and water polo events. The three sports of aquatics were held at Aquatic Centre in Sport Authority of Thailand Sport Complex, Bangkok, Thailand. Aquatics events was held between 9 December to 12 December.
| 100 m freestyle |  Ang Peng Siong | 52.42 | Oon Jin Gee | 53.44 |  Padhanaseth Changkasiri | 54.04 | |
| 200 m freestyle |  William Wilson | 1:57.25 | Oon Jin Gee | 1:57.63 |  Daniel Arief Budiman | 1:57.72 | |
| 400 m freestyle | William Wilson | 4:08.81 | René Concepcion | 4:13.64 | Daniel Arief Budiman | 4:13.84 | |
| 1500 m freestyle | William Wilson | 16:42.19 | Enrico Rosquillo | 17:08.45 |  Huang Ying Tsang | 17:19.20 | |
| 100 m backstroke | David Lim Fong Jock | 58.36 | Lukman Niode | 58.89 | Padhanaseth Changkasiri | 1:01.42 | |
| 200 m backstroke | David Lim Fong Jock | 2:08.86 | Lukman Niode | 2:09.06 | Eric Buhain | 2:13.56 | |
| 100 m breaststroke | Tjatur Sugiarto | 1:06.59 | René Concepcion | 1:06.83 | Jairulla Jaitulla | 1:06.84 | |
| 200 m breaststroke | Lee Concepcion | 2:24.56 | Francisco Guanco | 2:25.81 | Tjatur Sugiarto | 2:26.40 | |
| 100 m butterfly | Mustamsikin | 57.68 | Sudiono Sabeni | 57.77 | Ang Peng Siong | 57.79 | |
| 200 m butterfly | Daniel Arief Budiman | 2:09.29 | Mustamsikin | 2:10.51 | Renato Padronia | 2:10.85 | |
| 200 m individual medley | David Lim Fong Jock | 2:10.57 | Jairulla Jaitulla | 2:12.11 | Lukman Niode | 2:12.35 | |
| 400 m individual medley | Eric Buhain | 4:43.63 | René Concepcion | 4:44.19 | Soo-tho Kok Mun | 4:50.35 | |
| 4×100 m freestyle relay | Singapore Ang Peng Siong Tay Khoon Hean David Lim Fong Jock Oon Jin Teik | 3:34.60 | Indonesia Lukman Niode John David Item Daniel Arief Budiman Mustamskin | 3:38.82 | Philippines René Concepcion William Wilson Enrico Rosquillo Jairulla Jaitulla | 3:40.36 | |
| 4×200 m freestyle relay | Singapore David Lim Fong Jock Ang Peng Siong Oon Jin Gee Oon Jin Teik | 7:58.03 | Philippines René Concepcion William Wilson Enrico Rosquillo Lee Concepcion | 7:58.44 | Indonesia Lukman Niode Daniel Arief Budiman Mustamsikin Moh Iqbal Tawaqqal | 8:13.44 | |
| 4×100 m medley relay | Singapore David Lim Fong Jock Oon Jin Teik Ang Peng Siong Oon Jin Gee | 3:56.96 | Indonesia Tjatur Sugiarto Lukman Niode John David Item Mustamsikin | 3:58.17 | Philippines William Wilson Renato Padronia Eric Buhain Lee Concepcion | 4:02.82 | |
| 100 m freestyle | Nurul Huda Abdullah | 59.51 | May Tan Seok Khoon | 1:00.83 | Elfira Rosa Nasution | 1:00.95 | |
| 200 m freestyle | Nurul Huda Abdullah | 2:07.77 | Chatkaew Bulsuk | 2:10.13 | May Tan Seok Khoon | 2:10.45 | |
| 400 m freestyle | Nurul Huda Abdullah | 4:25.39 | Kusumarn Thammongkol | 4:30.33 | Elfira Rosa Nasution | 4:30.35 | |
| 800 m freestyle | Nurul Huda Abdullah | 8:58.29 | Kusumarn Thammongkol | 9:15.73 | Chatkaew Bulsuk | 9:17.87 | |
| 100 m backstroke | Ratna Laurentia Pradipta | 1:07.93 | Christine Jacob | 1:10.12 | Rizza Maniego | 1:11.36 | |
| 200 m backstroke | Ratna Laurentia Pradipta | 2:26.26 | Christine Jacob | 2:30.94 | Dullaya Phuangthong | 2:33.50 | |
| 100 m breaststroke | Nuntana Khaoplum | 1:16.39 | Rainy Maria Awuy | 1:16.82 | Rose Luzelle Papa | 1:20.24 | |
| 200 m breaststroke | Nuntana Khaoplum | 2:44.86 | Rainy Maria Awuy | 2:46.37 | Kanogwon Sriprasert | 2:53.73 | |
| 100 m butterfly | May Tan Seok Khoon | 1:04.97 | Nurul Huda Abdullah | 1:06.07 | Elfira Rosa Nasution | 1:06.94 | |
| 200 m butterfly | Nurul Huda Abdullah | 2:22.54 | May Tan Seok Khoon | 2:34.24 | Chutiporn Prypiroonroj | 2:34.24 | |
| 200 m individual medley | Nurul Huda Abdullah | 2:24.61 | Elfira Rosa Nasution | 2:27.09 | Kanongwon Sriprasert | 2:32.45 | |
| 400 m individual medley | Nurul Huda Abdullah | 5:01.19 | Elfira Rosa Nasution | 5:09.62 | Maya Masita Nasution | 5:19.25 | |
| 4×100 m freestyle relay | Thailand Chatkaew Bulsuk Papanee Jirathornwattana Kusumarn Thammamongkol Panachit Dhanasin | 4:06.70 | Philippines Christine Jacob Ma Christina Bautista Rose Luzelle Papa Celestial De Leon | 4:07.00 | Malaysia May Tan Seok Khoon Jutta Mee Poh Tan Marjorie Tan Suan Su Nurul Huda Abdullah | 4:10.55 | |
| 4×100 m medley relay | Indonesia Laurentia Ratna Pardipta Rainy Maria Awuy Elfira Rosa Nasution Yustina Atmadja | 4:32.64 | Thailand Dullaya Phuangthong Nuntana Khaoplum Kanogwong Sriprasert Papanee Jirathornwattana | 4:38.70 | Philippines Christine Jacob Rose Luzalle Papa Mari Kaar Maniego Ma Christina Bautista | 4:44.46 | |
| Men's springboard | Somchai Ongkasing | 556.41 | Kristedy Permana | 548.73 | Djawahir Moc Taufan | 547.17 |
| Men's platform | Somchai Ongkasing | 527.13 | Eko Setiawan Leoloes | 511.26 | Dody Wihaardjito | 460.62 |
| Women's springboard | Dwi Mariastuti | 434.94 |  Aye Aye Soe | 386.76 | Lee Po Ling | 363.63 |
| Women's platform | Indah Windyaningsih | 351.99 | Dwi Mariastuti | 346.41 | Aye Thuzar | 320.52 |