to pee in the shower or not to pee!
earlier this week, a caller told me i should pee in the shower because that saves water. is that true? inquiring minds want to know. so i spent an informative hour with our resident chatroomgod to figure out the truth, and present it here for everyone! the math is chatroomgod’s, but i did the research.
the debate is whether you should
a) shower and use the toilet separately.
b) shower and pee during your shower.
according to chatroomgod, your total water usage for these two activities is:
a) (s * r) + f
b) ( (s + (n*p) ) * r )
where:
s = time of your shower (without peeing included)
r = rate of your showerhead (i.e., how fast water is flowing)
n = non-overlap between peeing and other showering activities (0 = 100% overlap, 1 = no overlap)
p = time you spend peeing (assumed to be the same in or out of the shower)
f = amount of water in a single flush of the toilet (barring a fancy toilet that varies it somehow)
the time spent showering is the same in both situations, and can be subtracted from both, reducing them to this calculation of water usage for peeing only:
a) f
b) (n*p) * r
assuming that you stop everything in the shower and pee (n = 1), then for “b” to be more efficient than “a” (i.e., f > p * r):
f/r > p
that’s the math; now onward to my research!
to figure out “r”, what is the “average” flow rate of a showerhead? it depends on your water pressure, and that varies widely. i got sidetracked down that path for a while, but eventually gave up. the epa claims that standard showheads are 2.5 gallons per minute(gpm). older ones were upwards of 5gpm, but let’s use the 2.5 gpm number for now.
onward to figure out “f”, toilet flush volumes. the epa was less helpful this time, but wikipedia came to the rescue with an article that includes the epa standards for toilets. pre 1994, 3.4 gallons was typical; now 1.6 should be more then norm. personally i have an old toilet and a new showerhead, which is probably a common combination.
for reference, and for “p”, what are the average urination times? i found this study of urination times, but it’s just an abstract and kinda useless to me. i found this article on urine flow testing, which gives average rates but not total time. in the end i’ll go for here-say, rumor, and personal experience, which says anywhere from 20 to 60 seconds.
for a new showerhead and an old toilet, that means:
(3.4 / 2.5) > p, or 1.36 > p
that means that you could pee for 1.36 minutes (over 80 seconds) and still be more efficient in the shower! a clear win for shower-pee-ers everywhere!
if you have a newer toilet, then it’s a tougher competition:
(1.6 / 2.5) > p, or 0.64 > p
around 38 seconds of pee time before the new toilet is more efficient. That’s still quite a bit; shower-peeing still wins quite often.
so next time you take your slave into the shower to pee on them, do so with the warm glow of knowing that you are probably being green.