Windmill is one of few 'mechanisms' Amish accept unconditionally. Why? Because God created wind. Wind turns the mill. Mill pumps water. Logic is flawless.
Types
Water pump (most common): pumps water from well to tank on barn roof. Gravity feeds to house, stalls, troughs. Grain (rare): grinds flour. Sawmill (very rare): cuts boards.
Cost
$3,000-5,000 to install. $0 operation (wind is free). Lasts 30-50 years. Electric pump: $1,000 + $200/year electricity + replacement in 10 years. Over 30 years windmill saves $8,000-10,000.