Officers were alerted on Wednesday afternoon by a concerned neighbour who noticed the woman in her 80s was not answering her door for post and still had her curtains drawn.
PC Tom Matthews and student officer Tom Currin forced their way into the property in Aveley and heard the woman calling for help.
"The woman sadly has no nearby family or friends that are able to make regular visits to check on her," said PC Matthews.
"When we found the woman she told us that she'd been trapped in the bath for up to three days.
"This incident is an example on why it's essential to check on your elderly and vulnerable neighbours."
He added: "In this case a neighbour spotted a few minor things that were out of character and she rightly called for help.
"We would like to praise her for taking the time to consider the welfare of an elderly person within her community.
"When we arrived we could tell that something was wrong and we had no option to force entry to the property in order to help the woman, who was quickly assessed and taken to hospital."
The condition of the woman is not known.