When I have to use is + past participle and is + to be +past participle.
The water is poured. The water is to be poured.
Please help to differentiate.
The first sentence describes something that's actually happening.
The second sentence describes something that needs to be done, or is almost going to happen.
The water is poured (passive). Somebody pours the water (active).
The water is to be poured (passive). Somebody is to pour the water (active).
The first sentence, which is the present simple passive, shows that somebody always, regularly, or as a routine pours the water.
The second sentence is also in the present passive form, but it means that somebody intends or it's necessary for him to pour the water. It's indicative of an action that is going to happen.