Some children on the Autistic Spectrum are true water babies however they are also children on the spectrum that find bathing extremely stressful and bath time can be accompanied with lots of distress and tears,
If your child is the latter we would suggest not to have bath time as your pre-bedtime routine as this will only increase anxiety before bed (which is undesirable)
We would also suggest having the temperature of the water below the normal range, lukewarm tepid water works best for their sensitivities.
Some children have behaviours where they allow their bodies to become wet but the hands must remain dry at all times, it is advisable to have a dry towel present and in the sight of your child at all times to offer reassurance to them.
Your child may also be hypersensitive around the back of the neck, ears and top of their head, gently movement is advised when shampooing with minimal mild product, wiping a wet cloth over the head is better than pouring water over your child.
Laying down in the bath water may be too much for your child, try to encourage slowly sitting instead of allowing them to stand as they would be in danger of slipping and hurting themselves.
Some child suffer from separation anxiety. You may have to remain in the room way past the normal age range.
We would also advise not to bleach your bath to often because of the high toxicity content.
but remember to try to make bath time a fun experience.