Why swimming pool water get tested regularly? In swimming pool water may contain germs that can cause recreational water illness. These illness include stomach, ear and skin infections, but diarrhea is the most frequently reported illness, If it is not properly maintained the water in your domestic swimming pool may contain a range of germs, including bacteria and viruses. Some germs can cause health problems, that's why you should check your swimming pool water regularly to make sure that the water is safe for swimming. that's why swimming pool water testing regularly is beneficial.