To determine the optimal utilization of hybrid bonds relative to S&P Global Ratings' cap, we must compare the cost of hybrid bonds to the cost of equity. Companies use hybrid bonds to achieve a lower overall cost of capital (WACC) while still receiving partial equity credit from rating agencies like S&P, which protects their credit ratings.

1. **Cost of Debt and Hybrid Bonds:** 
Based on the market data for 2022, the average yield for investment-grade corporate bonds (iShares Core Euro Corp Bond) is 1.085%. The spread (Sub-Sen Delta) for subordinated non-financial investment-grade debt is 2.295%. 
Therefore, the estimated pre-tax cost of hybrid bonds is approximately 1.085% + 2.295% = 3.38%. Since interest on hybrid bonds is generally tax-deductible, the effective post-tax cost of hybrid debt would be even lower.

2. **Cost of Equity:**
Using the 10-year swap curve as a proxy for the risk-free rate (1.927% in 2022), plus a standard equity risk premium scaled by the company's beta, the cost of equity will typically fall between 6.5% and 9%. 

3. **Optimization:**
Because the cost of hybrid debt (~3.38% pre-tax) is significantly lower than the cost of equity, it is highly accretive for Veolia Environnement to replace the more expensive equity with cheaper hybrid debt. S&P allows up to 15% of total adjusted capital (Debt + Equity) to be composed of hybrid bonds while still attributing 50% equity credit to them. Issuing hybrids beyond this 15% cap would result in the excess being treated entirely as debt, eliminating the specific rating-agency equity benefits. 

To maximally reduce its Weighted Average Cost of Capital (WACC) without negatively impacting its recognized equity cushion under S&P's methodology, the company should fill this advantageous "bucket" entirely. 

Therefore, Veolia Environnement should utilize 100% of the S&P Global Ratings' cap.

<answer>100%</answer>