Instruction: Answer the given question by extracting information from the supporting document.

Input:
Question: What is the wattage of the bulb ?
Document: The bulb was broken upon receipt and this was not discovered until after the return date. The crystal was very fragile and you must turn it very carefully by hand until it no longer leaks, or it will break. I called Watts and they considered it a shipping issue and referred me back to Amazon. I chatted online with an Amazon rep and she shipped us an entire replacement unit because there are no dealers locally.
There should be warning labels all over it and there isn't.When I tried to install the water system for the second time I knew this time to plumb in a shut off valve with a bypass so that I didn't have to shut off the water to the whole house in case it didn't work the second time or for future repairs or replacement. When I VERY gently put it all together all was well until I slid the bulb into place. The weight of the bulb cracked the crystal.
The first package arrived damaged and the crystal tube was broken. Unfortunately I had already shut off my water and re-plumbed everything for the UV system, before I discovered the broken crystal. Was able to exchange it quickly and the second one arrived undamaged.The packaging for this is poor. The metal tube that holds everything is heavy and it is shipped in the same box as the bulb and the crystal tube. The only padding on the bulb and the crystal tube is a foam sleeve.
I just finished installing one of these on my home in Hawaii where we use rainwater catchment as our water source. I'm happy with both the quality and the price. I doesn't come with filters like many of the other UV units so you do need to add a filter and a pre-filter to the water line before it enters the UV unit. But even after adding two filters the price is still reasonable. The first unit arrived with a broken bulb but Amazon had a replacement to me within four days.
What a great little unit. Used on a circulation system with a pool system.This gives the end user confidence of risk free water at all times.
This product was shipped incomplete and unusable. I have tried to contact the supplier and all to no avail. Do not waste your money on the seller of this product. What a total waste of money. I even asked if I could pay extra to get the missing part and nothing, not even a reply.
There is an LED indicator and audible alarm (continuous beep). The instructions recommended a GFCI receptacle, however, I've hooked it to my APC Smart-UPS 1250 for disinfection during power outages since I'm downstream from the well house by about 250 feet.
The unit works well and cost significantly less than what was available to us in Hawaii. The 5 stars is because of the way Amazon handled the problem.
The flow direction suggestion concerned me due to the way the house is plumbed there is no way to provide clearance for lamp removal while mounting the curved/bell at the water ingress point without excessive/sloppy plumbing.The 'C' retention clips have a single screw hole in the center.I hope this review helps answer some of the questions that go unanswered. Best wishes from Alabama.
Note to Amazon: packing peanuts!
Answer: The output listed on the transformer/ballast is 20-40 watts.  UV bulbs are not rated as much by wattage, but rather by their output/sterilization abilities.  If you need additional information, you can contact Watts (manufacturer) customer service at: 1-978-689-6066, Monday - Friday (8:00am - 4:30pm EST).