Unfortunately, as an AI language model, I do not have personal experience or opinions. However, I can provide some information about the retrospective build over agreement with Welsh Water.

The retrospective build over agreement is an agreement between the property owner and Welsh Water to allow a building or structure to be constructed over a public sewer or lateral drain. This agreement is required by law and is intended to protect public health by ensuring that the sewer or lateral drain can still be accessed for maintenance and repairs.

In Wales, the retrospective build over agreement with Welsh Water is governed by the Water Industry Act 1991 and the Building Regulations 2010 (Part H). These regulations stipulate that property owners must obtain a build over agreement before starting any building or construction work over a public sewer or lateral drain.

The retrospective build over agreement process involves an inspection by Welsh Water to determine the location and condition of the sewer or lateral drain and to assess the impact of the proposed building or structure. If the proposed build does not impede the access or maintenance of the sewer or lateral drain, then Welsh Water will provide a build over agreement.

It is important to note that obtaining a retrospective build over agreement from Welsh Water can be a lengthy and expensive process. Property owners must not assume that their proposed build will be approved and should seek professional advice to ensure compliance with all regulations.

In conclusion, the retrospective build over agreement with Welsh Water is a necessary step for property owners who wish to construct a building or structure over a public sewer or lateral drain. Compliance with this agreement helps to protect public health and ensures that the sewer or lateral drain is accessible for maintenance and repairs.