My work for the Wildlife Conservation Board is to manage the Stream Flow Enhancement Program. This program has the goal of providing grants to fund projects that will increase the amount or quality or timing of water in the streams, rivers, and other watercourses of California.
One way of achieving this goal is to fund projects that change how water users use the water in waterways.
What does that mean?
Water is a very valuable, and highly regulated, resource in California. In this state, humans do not have free rein to use as much water as they want at any time that they want for whatever reason that they want from any watercourse that they want. Instead, to use water humans need to work within a system of water rights. This system serves to make sure that each water user (called diverters) along a watercourse gets the water they need, and that no other diverter takes water that is reserved for someone else.
The State Water Resource Control Board (SWRCB) is a state agency that was established in 1914 (a date that will be significant in a bit). The SWRCB oversees water rights, approves and tracks changes to water rights, makes sure that water users are complying with the terms of their right, and conducts other related activities.
Landowners and/or water diverters have a few options available to them for how to go about legally using water in a watercourse.

One way is to show that they have a Riparian Water Right. This means that a parcel of property has a watercourse of some kind on it or along a boarder, and the landowner has the right to use some of the water in that watercourse (how much and for what purpose still needs to be spelled out in their riparian water right, but the landowner will get to use some of that water). Riparian water rights do have some significant limitations. One is that the water that is diverted out of a watercourse under a riparian water right must be used on that same parcel of property. It cannot be pumped away to use on some other piece of land. A second is that water diverted under a riparian water right cannot be stored and used later. Many California water systems have much more water in the winter and spring then they do in the summer and fall. One strategy that some people use is to collect water during the wet periods of the year, store that water, and use it during the dry periods of the year. This cannot be done under a riparian water right. The water must be used immediately.
If a riparian water right in not available, a diverter needs to secure an Appropriative Water Right. These come in two forms. If water has been diverted since prior to 1914 (see I said that date was going to come up again) without any interruptions that lasted for more than five years, then that water use could be claimed under a Pre-1914 Appropriative Water Right. The water could have been used for different purposes and at different locations over that time, but it does need to be proved to have been used. A Pre-1914 Appropriative Water Right does not need to be approved by the SWRCB. Also, the diverter can change the exact location where water is being pulled out of a watercourse (called the Point of Diversion), the location of where the water is being used, and the purpose to which the water will be used for, all without requiring prior approval from the SWRCB. A downside is that is may be difficult to prove continuous use of water since before the year 1914, and so Pre-1914 Appropriative Water Rights are more often challenged in court.

If continuous use of water cannot be proved to date back to before 1914, a Post-1914 Appropriative Water Right will need to be obtained from the SWRCB. Post-1914 Appropriative Water Rights get complicated and nuanced. They can be acquired in one of two ways (registrations and permits/licenses), and each have numerous possible paths and varying requirements. However, while they are the most complex, difficult, time-consuming, and expensive, Post-1914 Appropriative Water Rights are also the most secure method for someone who wants to divert water out of a watercourse. These water rights are obtained from the SWRCB and are supported by various legal documents which make them difficult to challenge or overturn.
All water rights holders, regardless of the type of water right, must submit an annual Statement of Diversion and Use form with the SWRCB. These are publicly available documents that allow for the tracking and enforcement of water rights throughout the state.
Sometimes, changes need to be made to an existing water right. There are several paths that can be followed if a change is needed, and they depend on what type water right is involved and what type of changes are being sought, but that will be material for another post.
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