The complainant has requested information about the treatment of drinking water supply at a specific site. Southern Water Services Ltd (‘Southern Water’) refused part of the request under regulation 12(5)(a) of the EIR, which concerns national security or public safety. It disclosed some relevant information and advised it held no further information falling within scope of the request. The Commissioner has concluded that part 1 of the request should be interpreted more narrowly than Southern Water interpreted it. His decision is that Southern Water was not entitled to rely on regulation 12(5)(a) to withhold information falling within scope of part 1 of the request as he has interpreted it. The Commissioner’s decision is also that, on the balance of probabilities, Southern Water holds no further information falling within scope of part 2 of the request and complied with regulation 5 of the EIR. The Commissioner requires Southern Water to take the following step to ensure compliance with the legislation: Disclose the information held falling within the scope of part 1 of the request, namely information identifying the chemicals, substances and treatment processes introduced into the water supply serving the complainant's property during the period January to March 2021.