According to standard public health guidelines and recommendations under rural water supply schemes, the minimum safe distance between a drinking water well and any source of contamination (like soak pits, septic tanks, or drains) should be at least 15 to 30 meters or approximately 50 to 100 feet.
Practically, the minimum recommended is about 100 feet to ensure groundwater is not easily contaminated by seepage from nearby waste sources.
Therefore, option (4) — 100 feet — is the correct answer.