You have probably accidentally turned off the tap at the bottom of (under) the UltraStream. To check, remove the base plate with the 2 holes of the bottom of the UltraStream and see if the blue and white tap is on. When it’s on the tap will be in alignment with the hose.
If this is not the answer the filter may be blocked. If you are using rainwater which contains dirt due to lack of rain, this can block up the filter earlier than expected. It would be a good idea in this case to put a pre-filter for dirt before the UltraStream. The best filter for this job would be Polyspun pr paper available from our website. This filter is washable.