A male 45 years old wants his missing teeth to be replaced. Intraoral examination reveals Kennedy class 4 edentulous  maxillary arch. Impression is made with alginate.
The setting time of the material is affected by all of the following except:
Clinicians, however, can safely influence the setting time by altering the temperature of the water. The higher the temperature, the shorter is the setting time. The temperature of the mixing water should be controlled  carefully  within  a  degree  or  two  of  a  standard temperature,  usually  20  °C,  so  that  a  constant  and  reliable setting time can be obtained. In hot weather, special precautions should be taken to provide cool water for mixing so that premature gelation does not occur. It may even be necessary to precool the mixing bowl and spatula, especially when small amounts of impression material are to be mixed. 
Tap water naturally contains certain levels of metallic ions, primarily  calcium  and  magnesium.  It  has  been  shown  that compared with distilled water for mixing of alginate impression material, the use of tap water with a high hardness may accelerate the setting of the alginate. If one observes that the setting time has decreased in a new office or clinic location, the  effect  of  the  hardness  of  the  tap  water  on  setting  time should be considered as a possible cause.
Insufficient spatulation  results  in  failure  of  the  ingredients  to  dissolve  sufficiently. This leads to decrease in strength of the mix.
Reference:  Phillips’ science of dental materials / Kenneth J. Anusavice, Chiayi Shen, H. Ralph Rawls.—12th ed. Page no 174
Tap water
Temperature of the water
Hot weather
Insufficient spatulation