I stumbled across this place in May. I was really glad to find it at the time, and I am gratified to see it's still around and doing well, because it was new then and who knows how long it would last. I did laundry late at night my time and talked on the phone at times convenient to America.
Wonder Wash Self-Service Laundromat
No. 1 Lorong 23 Geylang Singapore 388352
Tel: +65.97862038 (although who this reaches isn't clear as there is no on-site staff; maybe it's for repair?)
MRT: Aljunied (East-West Line)
Buses: Geylang Road before Lorong 18 Geylang (stop number 80089),
Sims Avenue before Lorong 23 Geylang (stop number 80091),
Aljunied Road opposite SCN Centre (stop number 81231)
(Google Maps won't embed, so here's a link to the Google Map, with "1" actually marked on the Google Map on the street marked "Lorong 23 Geylang"--it's even in the right place!--as well as Wonder Wash's own map.)
Wonder Wash Coin Laundry has expanded its operations. This is excellent. Singapore doesn't have so many self-service laundries, and because of the high cost of labor sending your clothes out to get washed is expensive compared to surrounding countries. Wonder Wash says it's the only totally self-service retail laundry without an attendant in Singapore.
As someone who has visited a lot of laundromats/launderettes on four continents, I have to say this is one of the best. Not only is the place clean and the machines kept in excellent repair, but the machines include detergent automatically, so you don't have to bring your own.
It's S$4 (about $3) per load of 8 kg (17.5 pounds) for wash, and S$4 again for 40 minutes of drying, so a little higher than locally (in North America). I had to do a couple of drying cycles for jeans as the climate is quite damp. The machines do a fine job of getting clothes clean.
The new section in Unit 3 has larger capacity machines of up to 20 kg and also offers ozone cleaning, neither of which I've tried as they opened after I left. Also, the machines in Unit 1A which I used had no special settings for delicate loads; for that you should go to Unit 3.
It's in the red-light district, but it's a commentary on how safe Singapore is that the only effect this will have on you is that most of the restaurants in the neighborhood are open long into the wee hours of the morning. Geylang is known for excellent food, and some rather late-night nightlife, as well as some extremely obvious prostitution. But if you're staying elsewhere you'll want to check the bus schedules to and from the area, because Singapore's transit system doesn't run all night, except for a skeleton night bus service on weekend overnights. (Watch the traffic when you cross Geylang Road; it moves fast.)
Their latest news says they're expanding into residential estates which may in the future make them more convenient if you're not somewhere near Geylang.
Good machines, well-maintained, available 24/7. You can't really ask for much more.