India can only use 20% of water of Indus due to one of following treaty Indus water treaty, 1960.
The Indus Waters Treaty is a water-distribution treaty between India and Pakistan, brokered by the World Bank to use the water available in the Indus System of Rivers located in India. The Indus Waters Treaty (IWT) was signed in Karachi on September 19, 1960 by the first Prime Minister of India Pandit Jawaharlal Nehru and then President of Pakistan Ayub Khan.
According to this agreement, control over the water flowing in three "eastern" rivers of India — the Beas, the Ravi and the Sutlej with the mean flow of 33 million acre-feet (MAF) — was given to India, while control over the water flowing in three "western" rivers of India — the Indus, the Chenab and the Jhelum with the mean flow of 80 MAF — was given to Pakistan. More controversial, however, were the provisions on how the waters was to be shared. Since Pakistan's rivers receive more water flow from India, the treaty allowed India to use western rivers water for limited irrigation use and unrestricted use for power generation, domestic, industrial and non consumptive uses such as navigation, floating of property, fish culture, etc. while laying down precise regulations for India to build projects. The preamble of the treaty declares that the objectives of the treaty are recognizing rights & obligations of each country in settlement of optimum water use from the Indus System of Rivers in a spirit of goodwill, friendship and cooperation contrary to the fears of Pakistan that India could potentially create floods or droughts in Pakistan, especially at times of war since substantial water inflows of the Indus basin rivers are from India.