A water-treatment cartridge (3) for a water-treatment device, wherein the water-treatment device comprises a head with a port for feeding water for treatment to the cartridge and a port for discharging water from the cartridge (3) after treatment. The water-treatment cartridge (3) according to the invention comprises an inlet channel for feeding water for treatment to the cartridge (3) for making a fluid communication with the port of the head for feeding water for treatment to the water-treatment cartridge (3), and an outlet channel for discharging water after treatment from the water- treatment cartridge (3) for making a fluid communication with the port for discharging water after treatment from the water-treatment cartridge (3), at least one water-treatment bed, which the at least one water-treatment bed is in a fluid communication with the inlet channel for feeding water for treatment and with the outlet channel for discharging water after treatment. The water-treatment cartridge (3) is characterized in that it comprises orientating means (10) configured to make a flow of water for treatment from the port of the head for feeding water for treatment with the inlet channel, when the water-treatment cartridge (3) is installed in the head of the water-treatment device. The invention also relates to a head of a water- treatment device for use with a water-treatment cartridge (3). In addition, the invention relates to a water-treatment device comprising a head and a water-treatment cartridge (3).