Last updated September 9, 2017

iconWaterWhen for iOS

What is it?

A rule of thumb for lawncare is that most lawns require about an inch of water per week. Water too infrequently or too little, and the grass will probably not survive. Water too frequently, and the roots will remain shallow, making the grass vulnerable to drought and other problems.

WaterWhen helps by checking rainfall reports and forecasts for your area, and uses this data to find the next 1-week period that is expected to get less than 1 inch of rain. You can use this information to decide when to next water your lawn.

How do I use it?

When you first start WaterWhen, you will be prompted to fill in your zip code:

Once you supply the location, WaterWhen will begin retrieving rainfall data for your area - both historical and forecast. Please note that the initial weather data retrieval can take some time. Future updates usually require less data and are usually faster.

While weather information is being retrieved, you can specify when you last watered your lawn:

Once all the weather information has been retrieved, WaterWhen will give you a report:

If desired, you can view the day-by-day data that made up this report by tapping on the summary (e.g. "(0.86" rain expected the prior week)")

Where is the historical rainfall and forecast data coming from?

All weather data is retrieved from

Why does this app want Background App Refresh permission?

If permitted, WaterWhen will periodically refresh its weather data in the background, when you don't have the app open. This means that when you do open WaterWhen, a recommendation can usually be displayed immediately.

If you don't want to allow this, that's ok - WaterWhen will refresh its weather data the next time you open the app. However, depending on how long it has been since the last time you opened the app, you may need to wait for some time while weather data is retrieved before WaterWhen can display a recommendation.

What is this app not?

This app is one tool in assisting with lawn care. It is based on a rule of thumb that most lawns require approximately 1 inch of water per week. Please bear in mind the following limitations of this app:

In short - this app is not a foolproof way of keeping your lawn healthy. It is one tool to provide information to assist you in deciding how to care for your lawn.

Where can I get it?


If you have any questions about WaterWhen or encounter any problems using it, please contact me at waterwhen @