Aquatics at the 1981 Southeast Asian Games included swimming, diving and water polo events. The three sports of aquatics were held in Manila, Philippines. Aquatics events was held between 10 December to 13 December.
| 100 m freestyle |  Lukman Niode | 54.40 | Gerald Item | 54.80 |  Tay Khoon Hean | 55.56 | |
| 200 m freestyle |  William Wilson | 1:58.17 | Lukman Niode | 1:58.31 | Gerald Item | 2:00.28 | |
| 400 m freestyle | William Wilson | 4:11.68 | Soo Tho Kok Mun | 4:24.28 | Vicente Cheng | 4:24.65 | |
| 1500 m freestyle | William Wilson | 16:41.84 | Soo Tho Kok Mun | 17:16.30 | F. A. Goesarso | 17:36.84 | |
| 100 m backstroke | Lukman Niode | 1:01.13 | Richard Luna | 1:04.05 | David Lim Fong Jock | 1:04.32 | |
| 200 m backstroke | Lukman Niode | 2:15.82 | David Lim Fong Jock | 2:20.41 | Richard Luna | 2:22.78 | |
| 100 m breaststroke | Jairulla Jaitulla | 1:09.12 | Tjatur Sugiarto | 1:10.36 | Francisco Guanco | 1:10.62 | |
| 200 m breaststroke | Tjatur Sugiarto | 2:31.90 | Francisco Guanco | 2:32.06 | Jairulla Jaitulla | 2:32.49 | |
| 100 m butterfly | John Item | 1:00.54 | Renato Padronia | 1:00.85 | Gerald Item | 1:00.90 | |
| 200 m butterfly | John Item | 2:10.39 | William Wilson | 2:11.07 | Gerald Item | 2:11.20 | |
| 200 m individual medley | Gerald Item | 2:15.39 | Jairulla Jaitulla | 2:15.72 | Lukman Niode | 2:15.82 | |
| 400 m individual medley | Gerald Item | 4:47.76 | John Item | 4:50.60 | William Wilson | 4:50.80 | |
| 4 × 100 m freestyle relay | Indonesia | 3:41.46 | Singapore | 3:44.46 | Philippines | 3:46.81 | |
| 4 × 200 m freestyle relay | Indonesia | 8:11.56 | Philippines | 8:23.23 | Singapore | 8:23.64 | |
| 4 × 100 m medley relay | Indonesia | 4:06.47 | Philippines | 4:10.26 | Singapore | 4:12.26 | |
| 100 m freestyle |  Helen Chow Hiew Kee | 1:01.53 | Nanik Juliati | 1:02.99 | Christine Jacob | 1:03.71 | |
| 200 m freestyle | Junie Sng | 2:10.09 | Elfira Rosa Nasution | 2:17.87 | Katerina Ong | 2:18.71 | |
| 400 m freestyle | Junie Sng | 4:31.99 | Katerina Ong | 4:40.91 | Elfira Rosa Nasution | 4:45.54 | |
| 800 m freestyle | Junie Sng | 9:00.21 (rec) | Katerina Ong | 9:26.11 | Elfira Rosa Nasution | 9:49.79 | |
| 100 m backstroke | Helen Chow Hiew Kee | 1:09.92 | Nanik Juliati | 1:12.10 | Kwek Leng | 1:12.12 | |
| 200 m backstroke | Nanik Juliati | 2:31.77 | Kwek Leng | 2:32.27 | Pauline Wiwie | 2:36.04 | |
| 100 m breaststroke | Nanik Juliati | 1:18.95 | Helen Chow Hiew Kee | 1:19.37 | Sari Yulianti Saad | 1:20.21 | |
| 200 m breaststroke | Nanik Juliati | 2:52.20 | Sari Yulianti Saad | 2:56.07 | Ma Lourdes Samson | 2:56.46 | |
| 100 m butterfly | Junie Sng | 1:05.82 (rec) | Helen Chow Hiew Kee | 1:06.39 | Mavis Ee | 1:08.20 | |
| 200 m butterfly | Junie Sng | 2:21.20 | Nunung Selowati | 2:25.20 | Mavis Ee | 2:28.11 | |
| 200 m individual medley | Junie Sng | 2:27.55 | Helen Chow Hiew Kee | 2:28.27 | Nanik Juliati | 2:37.55 | |
| 400 m individual medley | Junie Sng | 5:05.70 (rec) | Helen Chow Hiew Kee | 5:11.58 | Mavis Eu | 5:34.42 | |
| 4 × 100 m freestyle relay | Indonesia | 4:15.80 | Singapore | 4:18.95 | Philippines | 4:21.06 | |
| 4 × 100 m medley relay | Indonesia | 4:44.38 | Singapore | 4:50.06 | Philippines | 4:52.98 | |
| Men's springboard 3 m | Kristendy Permana | 520.25 |  Sangwal Foungdee | 500.25 | Taufan Djawahir | 493.35 |
| Men's springboard | Kristendy Permana | 490.85 | Sangwal Foungdee | 454.70 | Haryo Ramayana | 398.45 |
| Men's | Eko Setiawan Lulus | 506.15 | Somchai Ongkasing | 474.15 | Teo Cheng Kiat | 426.20 |
| Men's platform | Somchai Ongkasing | 453.55 | Eko Setyawan Loeloes | 440.65 | Richard Tham | 415.60 |
| Women's springboard | Siani Ningsih | 373.00 | Lusiana Ambarwati | 331.50 | Annisa Tai | 322.00 |
| Women's springboard 3 m | Siani Ningsih | 416.25 | Lusiana Ambarwati | 407.70 | Annisa Tai | 253.05 |
| Women's | Siani Ningsih | 321.70 | Annisa Tai | 256.50 | Harli Ramayani | 193.75 |
| Women's platform | Siani Ningsih | 308.80 | Dwi Mariastuti | 294.26 | Not awarded (only 2 competitors) | |