[fewfews]

How to calculate the half-life of DMS in water?

[Borek]

Whatever the question really is, it is probably easier to measure.

[manofohm]

Do you have any data available to work with, or is this a curiosity?

[fewfews]

I want to make a mutagenesis with DMS but it reacts with water.The concentration must be under 1%.

[Arkcon]

Maybe someone who typically performs mutagensis on experimental organisms has a method, or a look-up table for the amount available in water over time.  I'd assume it would be made fresh, used rapidly, and destroyed before several half-lives pass, to be safe.  Maybe that have some input for you.  Although, if you don't have a defined plan of what you want to do and how you want to do it, playing with a mutagen seems very foolish.

[fewfews]

. playing with a mutagen seems very foolish.

Yes, I know.