Here is the design of a clinical trial:

Official Title: An Outcome Assessor-blinded Pilot Randomised Controlled Trial of an Ion-exchange Water Softener for the Prevention of Atopic Eczema in Neonates, With an Embedded Mechanistic Study

Included conditions:
- Atopic Eczema

Study Armgroups:
- {'label': 'Domestic ion-exchange water softener', 'type': 'EXPERIMENTAL', 'description': 'The intervention group will have a domestic ion-exchange water softener installed prior to birth.', 'interventionNames': ['Device: Domestic ion-exchange water softener']}
- {'label': 'Usual hard water supply', 'type': 'NO_INTERVENTION', 'description': 'The control group will receive their usual domestic water supply.'}

Interventions:
- {'type': 'DEVICE', 'name': 'Domestic ion-exchange water softener', 'description': 'Ion-exchange water softeners exchange calcium and magnesium, amongst other divalent cations, for monovalent sodium cations using a polystyrene resin. The sodium ions come from sodium chloride (common salt). The salt needs to be topped up every 3-4 weeks and sufficient quantities of block salt will be supplied to participants. The water softener used in this study does not require electricity and has two cylinders of resin which are used alternately. A control valve alternates the flow between the two cylinders and ensures a constant supply of regenerated resin. Ion-exchange water softeners typically reduce downstream water hardness to close to zero.', 'armGroupLabels': ['Domestic ion-exchange water softener']}

Primary Outcomes:
- {'measure': 'Proportion of eligible families screened who are willing and able to be randomised.', 'description': 'This is key to the determination of the likely success of a future, large-scale definitive randomised controlled trial (RCT).', 'timeFrame': 'Before birth'}

Please estimate the sample size based on the assumption: 
The study is a pilot and not powered to establish efficacy. It aims for a 95% confidence interval within 10 percentage points. Additionally, 27% of eligible families may not participate due to unsuitable home conditions.
Sample size
        This is a pilot study and therefore not powered to establish the efficacy of the intervention. A total of 80 families (40 per group) is judged to provide a sufficiently precise (within 10 percentage points for a 95% CI) estimate of the proportion of families who are willing to be randomised and who will go on to complete the trial.
        Findings from the Enquiring About Tolerance (EAT) study8 and the BEEP feasibility study24 allowed us to make a conservative estimate that approximately 70% of families screened will have a history of atopy that predisposes to a high risk of eczema in their offspring. Of these, 40%â60%âwould be expected to be willing and able to participate. Home factors also need to be considered: in SWET, 27% of eligible families could not participate because their home was not suitable for installation.16