Okay, let's tackle this question. The user is asking about the adequate water supply per person per day. Hmm, I need to recall the standard guidelines. From what I remember, the World Health Organization (WHO) has specific recommendations for water availability. Let me think... I think the WHO suggests a minimum of 20-50 liters per day for basic needs like drinking, cooking, and hygiene. But wait, what's the exact figure considered adequate? Maybe 50-100 liters is the standard for a better quality of life. Let me verify.

Wait, in some contexts, especially in public health or urban planning, the standard might be higher. For example, in urban areas, the supply might be around 135 liters per capita per day, but that's more for developed countries. However, the question is about what's considered adequate. The WHO's minimum is 20-50 liters, but adequate for a healthy life is probably higher. Maybe the answer is 135 liters? Or is there a different standard?

Alternatively, maybe the question is referring to the daily water requirement for the human body, which is about 2.5 liters, but that's not the supply. The supply per person per day for domestic use is different. Let me check some references. Oh right, the WHO and UNICEF's Joint Monitoring Programme for Water Supply and Sanitation (JMP) states that the minimum level is 20 liters per person per day. But adequate for a decent standard of living might be higher. However, in the context of MCQs, the commonly accepted answer is 50-100 liters per day per person. Wait, some sources say 135 liters is the standard in urban areas. Hmm, maybe the options here are different. Since the user hasn't provided the options, I need to infer based on standard knowledge.

Wait, the correct answer is supposed to be one of the options. Let me think again. If the question is asking for adequate supply, not just minimum, then the answer is likely 135 liters per day per person. That's the standard in many countries for urban areas. So, the correct answer would be 135 liters. Therefore, the explanation needs to mention WHO guidelines, the minimum vs adequate levels, and why the other options are incorrect. The wrong options might be lower than 20, or maybe 100 liters. Let me structure the explanation accordingly.

**Core Concept**
Adequate water supply per person per day is defined by the World Health Organization (WHO) as a minimum of **50-100 liters/day** for basic domestic needs (drinking, cooking, hygiene). Urban standards often require **135 liters/day** to meet sanitation and lifestyle demands. This reflects public health priorities and infrastructure benchmarks.

**Why the Correct Answer is Right**
The correct answer is **135 liters/day**. This figure aligns with urban water supply standards in developed nations, ensuring sufficient water for drinking (2-3 L), cooking (5-10 L), sanitation (50-100 L), and other domestic uses. It accounts for both physiological needs and practical hygiene, as recommended by the WHO and UNICEF for sustainable water management.

**Why Each Wrong Option is Incorrect**
**Option A:**

✓ Correct Answer: B. 150-200L