Water of the highest, cleanest class is classified as 'excellent'. 'At least sufficient' means that the water is generally of good quality and suitable for bathing, or the water meets minimum standards.
After water companies have treated sewage, they put cleaned and treated wastewater into lakes, rivers and the sea. The better the wastewater is treated, the better the quality of water for swimmers and the environment overall.
Even where the water meets the standards, sometimes water quality can be reduced, particularly after heavy rain, so please look out for temporary signs or information online that may advise against swimming.
Bacteria in the water can come from a number of sources, but the three main sources are: water draining from farms and towns during heavy rain; untreated sewage mixed with rainwater filling the system and overflowing into rivers and the sea (to prevent homes from flooding); and homes and businesses draining dirty water into the wrong pipes.
Interested in how rivers are protected?
Find out more about how your water company is protecting rivers. Don’t know who your supplier is? Find out here