In northern coastal Ecuador, water is routinely sold in 20 L reusable bottles for household consumption. These bottles are filled at central treatment facilities and distributed by private water companies. Similar bottled water markets are found in countries around the world. Commercially available bottled water offers an alternative source of drinking water in locations where piped infrastructure may be unsafe or non-existent. In this study we found that 73% (n = 94/128) of water sold in reusable containers in the Esmeraldas province of Ecuador was contaminated with coliform bacteria. In comparison, 25% (n = 9/36) of non-reusable bottles and 9% (n = 2/22) of water samples taken directly from the water treatment system contained coliform, suggesting that most observed bacterial contamination occurred due to inadequate cleaning of reusable bottles between use. The coliform contamination may pose a health risk to the Esmeraldas population. The present study may be indicative of similar situations in low- and middle-income countries around the world, given the widespread use of reusable bottles for water.