109:1 Matzah should only be kneaded with water that stood overnight, meaning that it was drawn at twilight and stood by itself all night. Even if the night is longer than twelve hours, one may not knead with this water until daylight. If the night is shorter than twelve hours until daylight, one must wait until twelve hours have passed from when the water was drawn. Unlearned people often knead at first light with the water that stood overnight even though twelve hours have not yet passed. Even though there are authorities upon whom they could rely, most authorities are stringent about this, therefore, one should be careful in this matter. (One may act leniently in a case of great need – Mishnah Brurah 455:6.) 109:2 If one can’t wait until twilight to draw the water, he may do so a little earlier so long as he doesn’t do so before sunset. (Twilight – bein hashmasos – is the period between sunset – shkias hachamah – and when the stars come out – tzeis hakochavim. It’s better to draw the water a little earlier than a little later – MB 455:5.) The accepted practice is to filter the water and to cover it; one must place the water in a cool spot and, when he carries it home in the daytime, he must be careful not to let the sun shine on it.