To estimate the Net Debt to EBITDA ratio for A2A S.p.A. based on the S&P (Standard & Poor's) Global Ratings methodology, we need to adjust the reported financial debt and EBITDA according to their standard criteria, which are widely tracked for utility companies. 

**1. S&P Adjusted Net Debt:**
S&P's methodology for Adjusted Net Debt includes standard financial debt while adding back debt-like obligations such as post-employment benefits (pensions) and asset retirement obligations (AROs), and deducting accessible cash and liquid short-term investments. 

- **Financial Liabilities:** 
  Other Noncurrent Financial Liabilities = 5,867,000,000 EUR
  Other Current Financial Liabilities = 1,022,000,000 EUR
  *Reported Debt = 6,889,000,000 EUR*

- **Debt-like Provisions (S&P adds these to debt):**
  Noncurrent Provisions For Employee Benefits (Pensions) = 248,000,000 EUR
  Other Longterm Provisions (Asset Retirement Obligations / Decommissioning) = 729,000,000 EUR
  *Total Adjusted Debt = 6,889,000,000 + 248,000,000 + 729,000,000 = 7,866,000,000 EUR*

- **Less Accessible Cash & Liquid Investments:**
  Cash And Cash Equivalents = 2,584,000,000 EUR
  Other Current Financial Assets (Short-term investments) = 14,000,000 EUR
  *Total Deductions = 2,598,000,000 EUR*

*Adjusted Net Debt = 7,866,000,000 - 2,598,000,000 = 5,268,000,000 EUR*

**2. EBITDA:**
S&P typically uses recurring Operating Income + Depreciation & Amortization (excluding one-off or non-recurring transactions).
- "Gross Operating Income EBITDA" explicitly equals 1,505,000,000 EUR. 
*(Note: Operating Profit of 687M + D&A of 818M = 1,505M; the non-recurring gain of 157M is correctly excluded).*

**3. Net Debt / EBITDA Ratio:**
Ratio = 5,268,000,000 EUR / 1,505,000,000 EUR = 3.500332...

<answer>3.5003322259136212</answer>