dear sir its called sankalpam fr snanam
its advisable to make sankalpam thru a sastrigal 1st occassion and then sub sequently u can continue to practice on your own
the very intresting thng is by doing ths sankalpam water in which you bathe bcomes purified and is equal to that of all sacred ones similar to ganges,kavery ,tamrabarani etc
aspproach aatrhthu wadyar fr more on ths