1 For surface waters, between 20 and 40 mm (upstream the strainer)  For municipal wastewater: for raw water, from 15 to 30 mm (but upstream from a straining and/ or lamellae settling process, fine screening is necessary); for sludge (if necessary), 10 mm or less.
Other studies. According to some studies, 18-year-old males have a refractory period of about 15 minutes, while those in their 70s take about 20 hours, with the average for all men being about a half-hour. Although rarer, some males exhibit no refractory period or a refractory period lasting less than 10 seconds.
What Is Very Light Period? Despite menstrual cycles vary from person to person, a normal period among women is approximately once in every 28 days. Typically, each period lasts from 4 to 7 days. During menstruation, the amount of lost blood ranges from 50 to 150 ml. Consequently, less than 50 milliliters may be considered a very light period. So, light periods are menstrual flows with unusually light occurance or rather short duration of blood loss.