Which pump method do you recommend for low flow sampling in small diameter wells (1-2 inches)?

When wells are two inches or larger, you have a wide variety of pumping methods you can choose from. For low flow purging and sampling you could use bladder pumps, electric submersible pumps (either 120-volt or 12-volt), piston pumps, and peristaltic pumps if the water is within about 25 feet of the ground surface. We have done a lot of comparisons of sampling devices over the years and haven’t been able to find a device that matches both the sampling accuracy and precision of the bladder pump as well as the long-term reliability. Bladder pumps are now available in diameters all the way down to 1/2-inch so you can get them into 3/4-inch casings (these are actually are slightly larger than 3/4). QED offers affordable pumps that fit down in 3/4-inch casings. When you get down to 1/2-inch direct push casings, you are faced with using something like a mechanical bladder pump in those applications. There is one company that does make an air-powered bladder pump down to 3/8-inch but, unfortunately, it didn’t pump very much water at all so it wasn’t very practical. Basically, you can use bladder pumps, peristaltic, electric submersibles and piston pumps in two-inch wells and then in smaller wells, bladder pumps are available down to 1/2-inch.