Was – Were. Wasn’t – Weren’t

Water was cold. Now it is hot.

They were hard. Now they are soft.

The weather wasn’t cold. But now it is cold!

Puppies weren’t big. But now they are big!

When we talk about Past we use WAS/WERE or WASN’T/WEREN’T.
For example: I was at school yesterday.

I, he, she, it – was/wasn’t
For example: She wasn’t at home yesterday. She was outside.

You, we, they – were, weren’t.
For example: They weren’t at home last week. They were on holiday.