A water treatment method includes: adding a chemical to water to be treated to obtain water to be treated which contains iodine and is provided with oxidizing power; and supplying the water to be treated that has undergone the chemical addition to an electrodeionization device (EDI device) to treat the water to be treated in the EDI device. At least a part of an ion exchanger filled in a deionization chamber of the EDI device is an anion exchanger.

A method for treating water in a spa or a hot tub includes, for example, suspending a water treatment dispenser from an upper end of a filter cartridge disposed in a skimmer of the spa or the hot tub. The dispenser includes a water treatment material. A supply of water is passed from the spa or the hot tub into the skimmer and through the filter cartridge so that the dispenser suspended in the filtered water in the filter cartridge is operable to dispense the water treatment material from the dispenser, and a supply of treated filtered water from the filter cartridge is returned to the spa or the hot tub. A cover, for example, may be employed when the dispenser is not used.

The invention provides a method of microbial control in water comprising adding to the water one or more bromine-based biocide(s) and cis-2-decenoic acid or a salt thereof. Compositions in the form of liquid concentrates comprising bromine-based biocides and cis-2-decenoic acid or a salt thereof are also described.

Examples herein include systems and methods for an improved disinfectant-dispensing device, such as a device that dispenses chlorine and/or bromine. An example embodiment can include a disinfectant-dispensing device with a chamber that holds solid disinfectant and includes an inlet and outlet. The device can also have a smart valve that includes an electric motor, a shaft, and a microcontroller. The electric motor can provide rotational motion to the shaft, which can extend or retract to allow or prevent the flow of water into the chamber. The microcontroller can operate the electric motor to control the shaft. The device can also include a battery that powers the electric motor and can be trickle charged via the low-power data channel. In one example, the microcontroller can receive a digital command from a pool controller on a low-power data channel and adjust the electric motor accordingly.