Regular Birth Pool In a Box Liner £36.50 Out of stock. If you wish to set your pool up and fill it with water to have a practise before baby is born then you will need a second liner. Many people choose to have a 'wet run' before their baby is born. If any water is left in the liner after the trial run then bacteria will begin to grow. We advised that you throw away the liner you used for your trial run and use a fresh, liner to give birth to your baby in.