In 2010 desalinated water is expected to provide approximately 25% of Israel's fresh water supply. Since desalination is cost-effective only if operated constantly, areas adjacent to the desalination plants may receive unblended desalinated water for prolonged times while other sources are added only at peak demand. Notwithstanding that desalinated water is of superior quality, it is widely accepted that soft waters may be corrosive to water distribution systems, and that soft waters mingling with other sources can cause a variety of adverse effects, namely metal corrosion and red water events. Despite this, no unambiguous quantitative criteria have been proposed to-date to address the required quality of desalinated water, following the post treatment stage. In this paper the water quality criteria are considered from various angles (chemical stability, bio-stability, effect on wastewater treatment, water palatability, health and economic effects, and post-treatment engineering considerations) and the following set of quality criteria for desalinated water is suggested: Alkalinity > 80, 80 < [Ca2+] < 120, 3 < CCPP < 10 (all concentrations in mg/L as CaCO3), and pH < 8.5. The work was carried out for, and approved by, the Committee for the Update of Water Quality Standards, appointed by the Israeli Ministry of Health.