According to Environment Agency summer water question testing, Sandgate has excellent bathing water quality. However these tests are actually conducted currently at Seabrook, 1.7km from the main Granville Parade beach most people would know as “Sandgate”.
You can see recent quality check results – they are marked as “Excellent” for 2025, 2024, 2023, and 2022.
https://environment.data.gov.uk/bwq/profiles/profile.html?site=ukj4208-13400
https://environment.data.gov.uk/bwq/profiles/data-samples.html?bw=ukj4208-13400#current
The tests are done to check compliance with standards set in the Bathing Water Directive. The Directive sets limits for a number of substances, and all countries in the EU have to ensure their popular beaches meet these standards.
Sandgate Parish Council have applied for Sandgate Granville Parade beach to be designated a bathing water. If that is successful, then there would also be regular water quality testing there.