a lot of/lots of

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much or many

These phrases are mainly used in informal English. lots of sounds a bit more informal than a lot of. Both forms are used in singular and in plural sentences.
It is not the phrase a lot of or lots of which determines singular or plural, but the subject of the sentence (here water and computers).

A lot of water is wasted. Lots of water is wasted.	singular
A lot of computers are needed at schools. Lots of computers are needed at schools.	plural

In formal English plenty of or much and many is used for a lot of/lots of.

Plenty of water is wasted. Much water is wasted.	singular
Plenty computers are needed at schools. Many computers are needed at schools.	plural