There is a public bus service morning and afternoon from Waterside to Stains railway station which is free to BA staff.

The public buses from Hatton Cross to T5 are also free to BA staff and not sure but these might also carry on past Waterside.

As you know there is a BA5 shuttle bus from T5 to Waterside and the BA1 which goes from West Base via Hatton Cross and T5 and Waterside through to Cargo. These depart freqyently from T5 to Waterside.

If you give the Waterside switchboard a call, they will know all the up to date bus services that are available to you.