The highly specialized technical nature of evaluating HWT against WHO performance recommendations necessitates testing in laboratories with advanced capabilities. In addition, appropriate safeguards must be in place to ensure the integrity of testing and the results. The full list of criteria is provided below.

1. Testing laboratories should preferably be institutions of which a department has been designated as a WHO Collaborating Centre (it being understood that the testing work would not be conducted by the institution as part of the WHO CC terms of reference or work plan).
2. The institution should be a not-for-profit, nationally or internationally recognized, ISO certified organization which conducts evaluations of household water treatment devices as part of its core activities. The institution should be independent of industry. Fees for the evaluation should be at cost. The institution should preferably be willing to waive the fees or set them at a lower level for those manufacturers of developing countries for whom the amount concerned represents an obstacle to participate in the Scheme.
3. The institution should have established procedures in place to ensure that the trade names of the manufacturers and the brand names of the products are blinded to those who conduct the actual testing.
4. The head of the institution and the staff responsible for the testing activities should be required to disclose potential conflicts of interest, and the institution should have adequate mechanisms in place to address and manage conflicts to the satisfaction of WHO.
5. The institution should have a stable income from its core activities. The workload associated with the WHO HWT Evaluation Scheme should comprise of no more than 25% of the total workload of the institution.
6. The institution should agree to use and strictly adhere to the agreed procedure, the harmonised testing protocols and the reporting templates for testing results developed for the Scheme.
7. The institution should agree to report the testing results to WHO no later than 90 days after receipt of the product documentation, device samples and funds to cover the testing costs.
8. The institution should enter into a standard agreement for all participating testing laboratories, to reflect the necessary arrangements, address confidentiality, ownership of the results by WHO, and other relevant requirements. Based on the criteria, two laboratories have been initially selected to conduct testing under the Scheme. These laboratories are: NSF International (USA) and KWR Watercycle Research Institute (Netherlands).

Division of labour between the designated laboratories is based on the relative proximity to the manufacturer of the product to be evaluated, equity in distribution of workload, and availability of the designated laboratory to complete the evaluation within the time required.