This morning (20/7) the HP 18, 19 and 21 postcodes had either no water or very low pressure, with some leaks being reported too.
Thames Water have announced the problems should be resolved, but are encouraging anyone who is still experiencing issues to get in touch with them.
You can do that here:https://www.thameswater.co.uk/help/report-a-problem
And for advice on if you have no water, visit https://www.thameswater.co.uk/help/emergencies/no-water-or-low-pressure