When water causes illness, it's most likely that the water was contaminated with fecal matter. According to Water.org, only 10 percent of all wastewater gets treated. This means the rest of it flows freely into our water — and our systems. Only 62 percent of the world’s population has access to improved sanitation. Experts estimate that if world water sanitation was improved, as much as one-tenth of the world’s global disease burden could be prevented.