To assess the extent Veolia Environnement should rely on hybrid bonds (hybrid debt), we consider the capital structure given in the data and typical corporate finance reasoning.

- The data shows significant noncurrent liabilities and high leverage after the Suez acquisition, with substantial noncurrent financial liabilities excluding concession liabilities (2023: 19.69b EUR) and noncurrent liabilities (2023: 29.23b EUR). This indicates a heavy leverage baseline.
- Equity Attributable To Owners Of Parent for 2023 is 12.2547b EUR, with total equity 14.8669b EUR and noncontrolling interests 2.6122b EUR. The debt load is large relative to equity, suggesting room for optimization via hybrid instruments to improve leverage without diluting equity.
- The notes show substantial changes in equity components across 2022-2023, including deeply subordinated securities (a typical hybrid capital instrument) within the equity section for both issued and contributed capital. For 2023, Deeply Subordinated Securities Member is 3.4963b EUR, and there is significant issuance/adjustment of deeply subordinated securities (2022-2023) totaling around 1.62b EUR in contributed capital from hybrid debt, with subsequent repayments of some amounts. This indicates active use of hybrid debt instruments in the capital structure.
- Hybrid bonds (perpetual or long-dated subordinated debt) typically help optimize the balance sheet by acting as equity-like instruments, improving leverage ratios (lower equity needs for same debt), while providing tax-deductible interest in many jurisdictions and potentially favorable regulatory treatment. Veolia has already used such instruments (Deeply Subordinated Securities) and adjustments in equity attributable to owners of the parent tied to these instruments, suggesting the company has experience with hybrids and uses them to manage leverage.
- Market environment data provided (swap curves, credit indices, etc.) show elevated interest rates and higher risk premia in 2022, which would affect the cost of capital. Hybrid debt, with its equity-like characteristics, can be attractive to manage cost of capital when interest rates are high and equity issuances are dilutive or costly. The company already uses it in moderate amounts (noted as significant but not dominant by the numbers given), indicating a strategy to balance debt and equity without excessive dilution.

Given the above, it seems reasonable for Veolia to rely on hybrid bonds to a meaningful extent to optimize leverage and maintain financial flexibility, but not to the maximum (which would risk stability due to fixed obligations and potential regulatory constraints). A moderate-to-high but not extreme share of hybrids is appropriate.

Conclusion: 50%

<answer>50%</answer>