The World Health Organization states that the below sources are not advisable to use as drinking water:

- Water from radiator circuits, hot water tanks (domestic heating systems)
- Water from toilet bowls or flush tanks
- Water from in waterbeds
- Water from swimming pools and spas

The chemicals and contaminants often found in swimming pools are many and most are toxic: pH+, pH-, alkalinity adjustment (bicarbonate of soda, muriatic acid, sodium bisulfate), calcium hardness increase, chlorine, bromine, biguanide, cyanuric acid, ammonia, bacteria and other pathogens, algae, insects, and animal waste...

The presence and levels of these chemical contaminants depend on numerous factors, including the type of pool, the type of disinfectants used and their dosage, the bather load, temperature, and pH.

Although Black Berkey® filters have been rigorously tested by independent third-party laboratories for the removal or reduction of numerous contaminants (herbicides, heavy metals, chlorine, chloramine, pathogenic bacteria, parasites, pesticides, perfluorinated acid compounds, petroleum products, pharmaceuticals, radiological products, trihalomethanes, viruses, and volatile organic compounds...) and even though the test data shows that chlorine concentration decreases by more than 99.9%, it is not recommended to filter water from your pool with Berkey® systems for frequent consumption.

This water could contain contaminants or chemicals other than those tested, for which there is no factual data regarding their safety.