Personally I believe the Single Most Constitutionally valid reason why Union of India had to carve out the State of Telangana is Water.
During the 58 years of Existence of Merged State of Andhra Pradesh from 1956 to 2014
Telangana Region was denied its fair share in both Krishna and Godavari River Waters in following ways
1. Entire focus was on Krishna River where availability is less than half of Godavari
2. Most in excess of 70% Krishna River Water allocated to Combined state was diverted to Andhra first and Rayala Seema later
3. Telangana was pushed into a 40 year 40 KM tunnel on Srisailam LEFT Bank that defies any common sense when same water could have been simply LIFTED from the point where KCR Govt now proposed that would have never taken even 4 years .. this was a deliberate FRAUD design that simply sucked time and money without giving drop of water to the parched region right on the bank of Krishna River
4. For decades people were made to believe LIFT irrigation is not viable and Gravity water not possible for Telangana
Many more similar mistakes net result is, NTR was more keen to Supply Water to Madras (now Chennai) ie over 1000 KM away which was his Karma Bhoomi than to millions of own state people on the Bank of River Krishna in Nalgonda and Mahaboobnagar both of which are Most Backward districts in India and the migration from Mahaboobnagar district to many parts of India for livelihood has left some villages deserted
Under such circumstances, then a Region Telangana now a state had no place other than the State Govt to get its grievance addressed, as the constitution does not allow a Region of a state to get the allocation directly from Central Govt nor Supreme Court can intervene.
Both Center and Supreme Court deal with State Government only not a Region of a state, in legal terms a Region does not have locus-standi to be a party in Water sharing dispute in a Tribunal or Supreme Court.
Though late, there was no alternate for Govt of India to address the problem without granting statehood to Telangana.
I know most of the people of Andhra Pradesh frankly acknowledge this in private if not going on record, I sincerely hoped with such a past Andhra Pradesh state will mend its past ways and make honest attempt to correct the past injustice and let Telangana have its fair share and work to make better use of Godavari Waters for common good as that is where the solution to both states lie.
Hence though AP called it Pattiseema what is essentially adding LIFT pumps to the Polavaram Right Canal that is almost ready which can potentially divert quickly 80 TMC water into Krishna, thought a Bold Good step is taken ignoring the terminology used and no notification to Godavari states Maharastra, Telangana, Chattisgarh and Odisha. I also liked the response from Telangana that simply made some oral comments as part of politics but did not do anything to stall the AP on the project.
Also Telangana Govt rightly so has embarked on taking thorough re-look into each and every project to re-engineer them to make the cost-effecting and faster on ROI and scrap part or full projects that was not in the interest of the state.
Sane thing for Andhra Pradesh would have been, not oppose the Project but work to conclude the water sharing mechanism from Srisailam before commissioning of the project to avoid operational hassles for which more than enough time is available.
instead AP has LOST the last option to partially redeem past mistake and it committed another mistake that will only make matters worse for AP for generations to come ..if it had any sense in realizing the ramifications of such insensitive and irresponsible letters as is seen by Telangana promptly sending counter letter to CWC on Polavaram Right Canal Pumping Station at Pattiseema where its case is stronger as the Award makes all diversions from Godavari to Krishna are to be shared