The risks associated with mosquito-borne diseases are real, but they are also simply a part of life in the tropics. One cannot expect to work in tropical regions applying mosquito repellent every few hours. If you are concerned about mosquito bites, wear long sleeves, long pants, and closed shoes. The trade-off might be that you'll be a little hotter, but at least DEET is not being diffused all over the immediate surroundings -- especially in an area where the locals directly depend on the natural resources around them for their livelihoods (using the river for drinking water, bathing, etc). DEET does not dissolve easily in water (<0.1g/100mL @ 20°C), and is potentially toxic to fish and humans.
Even when using DEET, there's no point in using 95%+ DEET. The costs of exposure to higher concentrations outweigh the benefits of its effectiveness as a repellent. The 7.0% works almost just as well. A better alternative is eucalyptus oil, or better yet... Victoria Secret's Bombshell perfume!
The chart below from the Journal of Insect Science shows different types of repellents and their effectiveness over time.