As Harvey, the largest rainstorm in the history of the continental United States, floods homes in Texas and Louisiana, many Americans want to send money for relief efforts.

The need for that help will be enormous: FEMA Administrator Brock Long has saidmore than 195,000 people already have registered for disaster assistance.

Many reputable organizationsalready are delivering food and care to those in need. But experts on charitable giving say donors need to be wary: con artists are also after your money. Scam charities raised hundreds of thousands of dollars in the aftermath of 2012's Hurricane Sandy, and they are likely to try it again now.

Here's are tips from legitimate sources, such as the Federal Trade Commission's web site, on how to safely donate to Harvey relief efforts.

Know where your money is going.

Contribute to organizations that have an experience assisting in disaster relief, and be skeptical of charities that pop up solely in response to Harvey or those with unfamiliar names. You can check out charities with the Better Business Bureau's (BBB) Wise Giving Alliance, Charity Navigator, Charity Watch, or GuideStar.

Never give out cash.

Give your donation by credit card or a check made payable to your charity of choice.

Understand crowdfunding.

Scammers may claim to represent legitimate organizations online. The crowdfunding website GoFundMe created a Medium post about safety measures being taken to protect those donating to relief efforts, and all verified GoFundMe Harvey-related campaigns as hosted at an official page.

Check a charity's website before you text a donation.

Confirm that the charity has authorized donations via text message — and keep in mind that your contribution may not reach the charity until after your phone bill is paid. It may be faster to donate directly to the charity.

Be wary of clicking on links or opening attachments in e-mails.

Unless you are sure you know who sent it, don't open attachments that could install malware on your computer. And don't assume that emails you get — or social media messages you see — have really been posted by the legitimate source. They might be fake.

Report suspicious organizations.

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