Heats
jeudi 9 août 2018, 03h00 GMT – 11h00 GMT
| Nom | Équipe | Temps | |
|---|---|---|---|
| 1 |  Katie Ledecky | United States | 8′ 9.13″ |
| 2 |  Ariarne Titmus | Australia | + 7.94″ |
| 3 |  Leah Smith | United States | + 8.08″ |
| 4 | Kiah Melverton | Australia | + 16.51″ |
| 5 | Erica Sullivan | United States | + 17.14″ |
| 6 | Haley Anderson | United States | + 18″ |
| 7 | Maddy Gough | Australia | + 18.15″ |
| 8 | Ashley Twichell | United States | + 20.23″ |
| 9 |  Waka Kobori | Japan | + 22.76″ |
| 10 | Mackenzie Padington | Canada | + 25.36″ |
| 11 | Chase Travis | United States | + 28.73″ |
| 12 | Yukimi Moriyama | Japan | + 32.31″ |
| 13 | Kate Sanderson | Canada | + 34.86″ |
| 14 | Ke Zhang | China | + 35.04″ |
| 15 | Nicole Oliva | Philippines | + 44.08″ |
| 16 | Rosalee Santa Ana | Philippines | + 1′ 2.91″ |
| 17 | Osisang Chilton | Palau | + 2′ 31.32″ |
| 18 | Mineri Gomez | Guam | + 2′ 49.2″ |