Why did my undersink UltraStream with benchtop faucet start leaking?

You may have used an NON VENTED under the sink faucet.
A vented faucet has 3 hoses coming from the faucet.  A non vented only has one hose.

Because the UltraStream makes molecular hydrogen (which is a gas) unless a vented faucet is used the UltraStream cannot breathe and so then will break.

Also a non vented faucet does not protect the UltraStream from the very high pressure of your mains water.  A vented faucet makes installation very safe as it turns the UltraStream off prior to going into the UltraStream.  This means if anything breaks then the only water that will be leaked is the water in the UltraStream and in the hoses (about 250ml)

You will need to purchase a vented faucet and install this in place of the non vented faucet.

Please be aware that our conditions of sale do not allow non-Alkaway under the sink faucets for this reason.

Also, we recommend that you place a high sided dish under your undersink UltraStream. Although we’ve designed it to avoid mains pressure, any water filter may leak. We’ve even seen cockroaches chew on hoses. So a dish under your UltraStream is a healthy precaution.