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.
Healthy normal Refractory period for men in their 40's - how much sex CAN you have? I am the wife asking this question. My husband is mid 40's. I know in his 20's, he could have sex/masterbation 2 times a day, maybe 3 , and I guess this is common, but what is normal for men in their 40's ? Is daily sex/masterbation too much generally? I am finding that -this is too much for him. Question for men in your 40's.