To determine the appropriate reliance on hybrid bonds for Veolia Environnement's capital structure, I need to consider several factors based on the provided data.

**1. Current Use of Hybrid Instruments**
- The balance sheet shows “Titres Super Subordonnés à Durée Indéterminée” (Deeply Subordinated Securities), which are hybrid bonds.
- In 2022 (2023-01-01), these stood at €3,496m, up from €2,461m at the end of 2021, largely due to the acquisition of Suez (€1,624m contribution noted in equity movements).
- They are classified within equity, but represent a significant fixed charge (coupons paid: €88m in FY2022 vs €24m in FY2021).
- Total Equity was €14,867m, so hybrids already represent about **23.5%** of total equity (or ~28.5% of parent equity €12,255m).

**2. Capital Structure and Leverage**
- Total Assets: €73,304m.
- Total Equity (incl. hybrids): €14,867m.
- Non-current financial liabilities (excl. lease/concession): €19,692m.
- Current financial liabilities (excl. lease/concession): €6,521m.
- Total gross financial debt (excl. hybrids) is quite high. Net financial debt is likely substantial (Cash ~€9,012m, but a lot of gross debt).
- The equity cushion (without hybrids) is lower. Removing hybrids (€3,496m) leaves Equity attributable to owners at ~€8,759m, implying a leverage ratio that would be much higher.

**3. Earnings Coverage**
- Operating Income after JV/Assoc. (Résultat Opérationnel): €2,333m.
- Net Finance Costs: -€633m in 2022 (up significantly from -€343m in 2021).
- Profit for the period: €998m; attributable to parent: €716m.
- Hybrid coupons: €88m. Coverage by earnings is reasonable (over 8x by OpInc, ~8x by net income).
- The interest rate environment has shifted: 5Y Swap averaged 1.73% in 2022 (up from -0.26% in 2021). Corporate bond yields (iShares index) rose from 0.73% to 1.09%. Subordinated yields (with 0.2 delta) rose from 1.30% to 2.30%. Cost of hybrid debt is increasing, making it more expensive relative to senior debt.

**4. Business Profile and Cash Flow Stability**
- Veolia is a utility/essential services company with stable cash flows (Operating Cash Flow from continuing ops: €4,104m in 2022 vs €3,164m in 2021).
- Operating WCR change is manageable.
- High tangible assets (PP&E €16,569m, Concession intangibles €5,292m).
- Stability supports some reliance on fixed-income hybrid securities, but the rising rate environment and the Suez integration risks (goodwill €11,638m, significant non-controlling interests now at €2,612m) argue for prudence.

**5. Optimal Mix Consideration**
- 0%: Too conservative; ignores the equity credit benefit and the large infrastructure base.
- 25%: Roughly current level (as % of total parent equity). The company has already reached this.
- 50%: Would mean hybrids of ~€6,000m–€7,000m, doubling down. In a rising rate environment, this would significantly increase fixed coupon obligations and possibly exceed rating agency tolerance for equity credit.
- 75%–100%: Extremely aggressive, highly unlikely for an IG-rated utility with acquisition-related goodwill and integration risk. Rating agencies would likely view excessive hybrids as a sign of financial engineering weakness.

**6. Market Context (Rates)**
- The shift from negative to positive euro swap rates (2021 avg 10Y: 0.05% vs 2022 avg: 1.93%) means newly issued hybrids would have higher coupons than the legacy ones from the negative-rate era.
- The sub-senior spread (delta 0.2 over IG index) averages ~2.3% in 2022, making the cost of hybrid capital materially higher.

**Conclusion**
Given Veolia is already near 25% reliance (hybrids as a proportion of its reported equity), the rising rate cycle, and the need to deleverage post-Suez acquisition, a target of **25%** is sensible. It maintains the equity credit without over-burdening the interest charge. Further increasing hybrids would be imprudent in the current market environment.

<answer>25%</answer>