Stir strawberries (already mashed) and sugar together, mixing thoroughly. Set aside.
Stir powdered fruit pectin with water in a saucepan. Bring to a boil, stirring constantly. Boil for one minute.
Stir mixtures together until sugar is completely dissolved and no longer grainy. Pour into clean dry containers, filling to within 1/2 inch of tops.
Cover at once with tight lids. Let stand at room temperature overnight. (We did it for about 12 hours.) Store in freezer until opened; then store in refrigerator.
Notes
Measure sugar exactly and do not reduce amount or jam will not set properly.I have included an alternate method that doesn't involve any cooking/boiling below.